High CPU when running in MAC

### Step 1: Please describe your environment

* ZeroNet version: Version: 0.6.2 r3467, Python 2.7.14 (default, Dec 25 2017, 15:20:24)
* Operating system: MAC OSX 10.13.4
* Web browser: Chrome Version 66.0.3359.139 (Official Build) (64-bit)
* Tor status: not available
* Opened port: yes
* Special configuration:

### Step 2: Describe the problem:
Just run zeronet by cmd `./zeronet.py` and look around for a while, the CPU will be 100% high.

#### Steps to reproduce:
The following is the running Log in shell console:

```
- Starting ZeroNet...
[10:47:52] - OpenSSL loaded, version: 020000000
[10:47:52] - Version: 0.6.2 r3467, Python 2.7.14 (default, Dec 25 2017, 15:20:24)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)], Gevent: 1.3.0
[10:47:52] - Creating FileServer....
[10:47:52] - Creating UiServer....
[10:47:52] SiteManager Deleting orphan site from content.db: 1LXgC6GXAc535zw8gLQbZpXnfoXNGkQDjh
[10:47:52] - Removing old SSL certs...
[10:47:52] - Starting servers....
[10:47:52] Ui.UiServer --------------------------------------
[10:47:52] Ui.UiServer Web interface: http://127.0.0.1:43110/
[10:47:52] Ui.UiServer --------------------------------------
[10:47:54] TorManager Connecting to Tor Controller 127.0.0.1:9051
[10:47:54] TorManager Starting self-bundled Tor, due to Tor proxy port 127.0.0.1:9050 check error: No connection
[10:47:55] ConnServer Checking port 26280 using portchecker.co...
[10:48:09] ConnServer Internet offline
[10:48:15] ConnServer Checking port 26280 using canyouseeme.org...
[10:48:19] Db:TestDb Table keyvalue outdated...version: False need: 1, rebuilding...
[10:48:19] Db:TestDb Table json outdated...version: 0 need: 1, rebuilding...
[10:48:19] Db:TestDb Table test outdated...version: 0 need: 1426195822, rebuilding...
[10:48:25] ConnServer [BAD :(] Port closed: Error: I could not see your service on 36.149.68.249 on port (26280) Reason: Connection timed out
[10:48:25] ConnServer Trying to open port using UpnpPunch...
[10:48:25] ConnServer Checking port 26280 using portchecker.co...
[10:48:45] ConnServer Checking port 26280 using canyouseeme.org...
[10:48:54] ConnServer [BAD :(] Port closed: Error: I could not see your service on 36.149.68.249 on port (26280) Reason: Connection timed out
[10:48:54] ConnServer Upnp mapping failed :( Please forward port 26280 on your router to your ipaddress
[10:48:55] ConnServer Internet online
[10:48:56] ConnServer Checking port 26280 using portchecker.co...
[10:49:16] ConnServer Checking port 26280 using canyouseeme.org...
[10:49:25] ConnServer [BAD :(] Port closed: Error: I could not see your service on 36.149.68.249 on port (26280) Reason: Connection timed out
[10:49:25] ConnServer Trying to open port using UpnpPunch...
[10:49:27] ConnServer Checking port 26280 using portchecker.co...
[10:49:47] ConnServer Checking port 26280 using canyouseeme.org...
[10:49:56] ConnServer [BAD :(] Port closed: Error: I could not see your service on 36.149.68.249 on port (26280) Reason: Connection timed out
[10:49:56] ConnServer Upnp mapping failed :( Please forward port 26280 on your router to your ipaddress
[10:50:52] Site:1MeFqF..q7nH Json merged-ZeroMe/1UDbADib99KE9d3qZ87NqJF2QLTHmMkoV/data/userdb/1DtTF9bsZgRRsqvsZo2V88rHRDz1rutWgr/content.json load error: TypeError: 'unicode' object does not support item assignment in SiteStorage.py line 295 > MutePlugin.py line 126 > SiteStorage.py line 90 > Db.py line 363
[10:52:24] Site:1MeFqF..q7nH Json merged-ZeroMe/1UDbADib99KE9d3qZ87NqJF2QLTHmMkoV/data/userdb/1L2xnwgpnyv2Si5C1nQNDxmaB6tzabXEnN/content.json load error: TypeError: 'unicode' object does not support item assignment in SiteStorage.py line 295 > MutePlugin.py line 126 > SiteStorage.py line 90 > Db.py line 363
[10:57:11] Site:1MeFqF..q7nH data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json fileGet error: [Errno 2] No such file or directory: u'data/1SunAWK2VUT9GQK32MpwRfFPVgcBSJN9a/data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json'
[10:57:11] Site:1SunAW..JN9a File data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json not exist yet, loading default values...
[10:57:11] Site:1SunAW..JN9a Extending content.json with: cert_auth_type
[10:57:11] Site:1SunAW..JN9a Extending content.json with: cert_user_id
[10:57:11] Site:1SunAW..JN9a Extending content.json with: cert_sign
[10:57:11] Site:1SunAW..JN9a Opening site data directory: data/1SunAWK2VUT9GQK32MpwRfFPVgcBSJN9a/data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/...
[10:57:11] Site:1SunAW..JN9a - data.json
[10:57:11] Site:1SunAW..JN9a Adding timestamp and sha512sums to new content.json...
[10:57:11] Site:1SunAW..JN9a Verifying private key...
[10:57:11] Site:1SunAW..JN9a Correct 1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ in valid signers: [u'1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ', u'1SunAWK2VUT9GQK32MpwRfFPVgcBSJN9a']
[10:57:11] Site:1SunAW..JN9a Signing data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:12] Site:1SunAW..JN9a Saving to data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:12] Site:1SunAW..JN9a File data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json signed!
[10:57:12] Site:1SunAW..JN9a Publishing data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 5/11 peers (connected: 11) diffs: [] (0.00k)...
[10:57:12] Site:1SunAW..JN9a [OK] 144.48.7.45:22488: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 1/5
[10:57:12] Site:1SunAW..JN9a [OK] 113.116.143.102:30875: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 2/5
[10:57:12] Site:1SunAW..JN9a [OK] 182.167.187.118:13799: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 3/5
[10:57:12] Site:1SunAW..JN9a [OK] 173.168.230.5:26640: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 4/5
[10:57:12] Site:1SunAW..JN9a [OK] 14.104.85.193:30181: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 5/5
[10:57:12] Site:1SunAW..JN9a Published data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 5 peers, publishing to 5 more peers in the background
[10:57:12] Site:1SunAW..JN9a [OK] 217.73.80.208:37352: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 6/5
[10:57:13] Site:1MeFqF..q7nH data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json fileGet error: [Errno 2] No such file or directory: u'data/1UDbADib99KE9d3qZ87NqJF2QLTHmMkoV/data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json'
[10:57:13] Site:1UDbAD..MkoV Extending content.json with: cert_auth_type
[10:57:13] Site:1UDbAD..MkoV Extending content.json with: cert_user_id
[10:57:13] Site:1UDbAD..MkoV Extending content.json with: cert_sign
[10:57:13] Site:1UDbAD..MkoV Opening site data directory: data/1UDbADib99KE9d3qZ87NqJF2QLTHmMkoV/data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/...
[10:57:13] Site:1UDbAD..MkoV - [SKIPPED] content.json
[10:57:13] Site:1UDbAD..MkoV Adding timestamp and sha512sums to new content.json...
[10:57:13] Site:1UDbAD..MkoV Verifying private key...
[10:57:13] Site:1UDbAD..MkoV Correct 1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ in valid signers: [u'1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ', u'1UDbADib99KE9d3qZ87NqJF2QLTHmMkoV']
[10:57:13] Site:1UDbAD..MkoV Signing data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:13] Site:1UDbAD..MkoV Saving to data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:13] Site:1UDbAD..MkoV File data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json signed!
[10:57:13] Site:1UDbAD..MkoV Publishing data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 5/75 peers (connected: 16) diffs: [] (0.00k)...
[10:57:13] Site:1SunAW..JN9a [OK] 90.186.229.47:11632: File not changed 7/5
[10:57:13] Site:1UDbAD..MkoV [OK] 120.79.35.235:38692: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 1/5
[10:57:13] Site:1SunAW..JN9a [OK] 73.24.158.188:15441: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 8/10
[10:57:13] Site:1UDbAD..MkoV [OK] 115.222.194.81:15441: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 2/5
[10:57:13] Site:1SunAW..JN9a [OK] 212.24.103.49:29535: File not changed 9/10
[10:57:13] Site:1UDbAD..MkoV [OK] 182.167.187.118:13799: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 3/5
[10:57:13] Site:1UDbAD..MkoV [OK] 139.162.241.69:15441: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 4/5
[10:57:13] Site:1UDbAD..MkoV [OK] 120.39.68.125:21028: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 5/5
[10:57:13] Site:1UDbAD..MkoV Published data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 5 peers, publishing to 5 more peers in the background
[10:57:13] Site:1UDbAD..MkoV [OK] 82.216.122.87:31305: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 6/5
[10:57:13] Site:1UDbAD..MkoV [OK] 58.57.82.170:15441: File not changed 7/10
[10:57:13] Site:1UDbAD..MkoV [OK] 185.107.169.23:15441: File not changed 8/5
[10:57:13] Site:1UDbAD..MkoV [OK] 180.154.105.39:15412: Thanks, file data/userdb/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 9/10
[10:57:13] Site:1SunAW..JN9a [OK] 24.54.1.63:36966: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 10/5
[10:57:13] Site:1UDbAD..MkoV [OK] 139.162.248.13:15441: File not changed 10/10
[10:57:13] Site:1UDbAD..MkoV [OK] 217.73.80.208:37352: File not changed 11/10
[10:57:22] Site:1SunAW..JN9a [FAILED] 85.192.155.142:28548: {'exception': 'Timeout'}
[10:57:33] Site:1SunAW..JN9a Opening site data directory: data/1SunAWK2VUT9GQK32MpwRfFPVgcBSJN9a/data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/...
[10:57:33] Site:1SunAW..JN9a - [SKIPPED] content.json
[10:57:33] Site:1SunAW..JN9a - [SKIPPED] data.json-old
[10:57:33] Site:1SunAW..JN9a - data.json
[10:57:33] Site:1SunAW..JN9a Adding timestamp and sha512sums to new content.json...
[10:57:33] Site:1SunAW..JN9a Verifying private key...
[10:57:33] Site:1SunAW..JN9a Correct 1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ in valid signers: [u'1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ', u'1SunAWK2VUT9GQK32MpwRfFPVgcBSJN9a']
[10:57:33] Site:1SunAW..JN9a Signing data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:33] Site:1SunAW..JN9a Saving to data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json...
[10:57:33] Site:1SunAW..JN9a File data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json signed!
[10:57:41] Site:1SunAW..JN9a Publishing data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 5/10 peers (connected: 10) diffs: [u'data.json'] (0.27k)...
[10:57:42] Site:1SunAW..JN9a [OK] 113.116.143.102:30875: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 1/5
[10:57:42] Site:1SunAW..JN9a [OK] 144.48.7.45:22488: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 2/5
[10:57:42] Site:1SunAW..JN9a [OK] 182.167.187.118:13799: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 3/5
[10:57:42] Site:1SunAW..JN9a [OK] 14.104.85.193:30181: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 4/5
[10:57:42] Site:1SunAW..JN9a [OK] 173.168.230.5:26640: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 5/5
[10:57:42] Site:1SunAW..JN9a [OK] 24.54.1.63:36966: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 6/5
[10:57:42] Site:1SunAW..JN9a Published data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json to 6 peers, publishing to 5 more peers in the background
[10:57:42] Site:1SunAW..JN9a [OK] 90.186.229.47:11632: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 7/5
[10:57:42] Site:1SunAW..JN9a [OK] 217.73.80.208:37352: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 8/5
[10:57:42] Site:1SunAW..JN9a [OK] 73.24.158.188:15441: Thanks, file data/users/1JYUntQYuGh1jELFnQxr1qUkk1PixYoLNQ/content.json updated! 9/5
[10:57:42] Site:1SunAW..JN9a [OK] 212.24.103.49:29535: File not changed 10/10
[10:57:54] Db:TestDb Table keyvalue outdated...version: False need: 1, rebuilding...
[10:57:54] Db:TestDb Table json outdated...version: 0 need: 1, rebuilding...
[10:57:54] Db:TestDb Table test outdated...version: 0 need: 1426195822, rebuilding...
```

#### Observed Results:

The recent debug log:

```
[2018-05-18 10:47:52,023] DEBUG PluginManager Loading plugin: AnnounceLocal
[2018-05-18 10:47:52,068] DEBUG PluginManager New plugin registered to: SiteAnnouncer
[2018-05-18 10:47:52,068] DEBUG PluginManager New plugin registered to: FileServer
[2018-05-18 10:47:52,068] DEBUG PluginManager New plugin registered to: ConfigPlugin
[2018-05-18 10:47:52,069] DEBUG PluginManager Loading plugin: AnnounceZero
[2018-05-18 10:47:52,075] DEBUG PluginManager New plugin registered to: SiteAnnouncer
[2018-05-18 10:47:52,075] DEBUG PluginManager Loading plugin: Bigfile
[2018-05-18 10:47:52,090] DEBUG PluginManager New plugin registered to: UiRequest
[2018-05-18 10:47:52,090] DEBUG PluginManager New plugin registered to: UiWebsocket
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: ContentManager
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: SiteStorage
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: WorkerManager
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: FileRequest
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: Peer
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: Site
[2018-05-18 10:47:52,091] DEBUG PluginManager New plugin registered to: ConfigPlugin
[2018-05-18 10:47:52,092] DEBUG PluginManager Loading plugin: Chart
[2018-05-18 10:47:52,137] DEBUG Db:Chart Connected to data/chart.db in 0.006s (opened: 1, sqlite version: 2.6.0)...
[2018-05-18 10:47:52,139] DEBUG Db:Chart Db check done in 0.008s, changed tables: []
[2018-05-18 10:47:52,140] DEBUG PluginManager New plugin registered to: SiteManager
[2018-05-18 10:47:52,141] DEBUG PluginManager New plugin registered to: UiWebsocket
[2018-05-18 10:47:52,141] DEBUG PluginManager Loading plugin: Cors
[2018-05-18 10:47:52,152] DEBUG - Translate file not exists: src/Translate/languages/en.json
[2018-05-18 10:47:52,152] DEBUG - Translate file not exists: plugins/Cors/languages/en.json
[2018-05-18 10:47:52,152] DEBUG PluginManager New plugin registered to: UiWebsocket
[2018-05-18 10:47:52,153] DEBUG PluginManager New plugin registered to: UiRequest
[2018-05-18 10:47:52,153] DEBUG PluginManager Loading plugin: CryptMessage
[2018-05-18 10:47:52,217] DEBUG - Opening /usr/lib/libssl.dylib...
[2018-05-18 10:47:52,217] DEBUG - Disabled SSL compression on
[2018-05-18 10:47:52,218] DEBUG - Missing SSLwrap, readded.
[2018-05-18 10:47:52,218] DEBUG - Python SSL version: OpenSSL 1.0.2n 7 Dec 2017
[2018-05-18 10:47:52,219] DEBUG - opensslVerify loaded:
[2018-05-18 10:47:52,227] INFO - OpenSSL loaded, version: 020000000
....
```

#### Expected Results:

* CPU should not keep 100% high

Reproduce the report by running ./zeronet.py on macOS and observe CPU use alongside the logged ConnServer and TorManager activity. Start by tracing the paths mentioned in SiteStorage.py, MutePlugin.py, and Db.py, then identify the operation that remains active; done means sustained CPU use is no longer abnormally high without breaking the reported site and network behavior.

索引モデルが issue の本文から書いたものです。