Extremely sluggish propagation of the optional files to peers

### Step 1: Please describe your environment

* ZeroNet version: rev4528
* Operating system: W10
* Web browser: FF beta
* Tor status: available
* Opened port: yes

### Step 2: Describe the problem:

Sorry for yet another whinning, but i have to as it seems like an issue that have to be fixed. I have published post on Millchan (famous zeronet site) with a few files attached (some were bigfiles no bigger than 10MB each)
Because i know how bad zeronet can sometimes be in seeding/downloading i have opened that poSt on three other servers each located in different location and each server has open poRt and clicked to seed all files of that post. In recent hours i was repeating the seed all request on that post on three servers as i was seeing servers has problems to download files of that post, only some files, some parts was downloaded. After around 6 hours like only half of the content was downloaded by my servers and it is not like all servers downloaded same parts, one has full file, other 0% of same file, etc. And it is just under 20MB total size of the files and my seeder connectivity is not bad + open port. That 3 servers hosts millchan and indeed maybe hundred/s of images/files on it while maybe another hundred/s of optional files are queued for download or being "paused" due to no peer.

On the host who published mentioned post, there is alot of content downloaded/uploaded. ZN directory has 5 million files and quite significant data transfer during previous hours. Zeronet is slow past years and swapping the computer after maybe 1-2 days of runtime. The CPU and HDD iops does not seem to be the bottleneck. If it is connection limit somewhere then zeronet users should be instructed (via ZN interface) to modify the limits or apply patch. If it can not be modified then zeronet should be supplied with the special browser that has no such limits.

Mentioned terribly slow propagation of the content is tragedy. Something has to be done about this so Zeronet can grow and people stay using it and do not giveup being too annoyed of the slowness. Thank you for the Zeronet, think about ways to allow it to go to the next level regarding performance.

まず、ZeroNet rev4528 について記載されているオプショナルファイルの伝播シナリオを、ここで報告されている3つのピア、開放ポート、およそ20MBのファイルを使って再現します。ソースファイルやテストは指定されていないため、ボトルネックを特定するために、ピアのシーディングとダウンロードの経路を追跡してください。伝播が測定可能な形で改善され、その挙動が回帰テストまたは文書化されたベンチマークでカバーされれば完了です。

索引モデルが issue の本文から書いたものです。