module 'main' has no attribute 'file_server' in greenlet.py; AttributeError: 'Config' object has no attribute 'optional_limit'

### Step 1: Please describe your environment

* ZeroNet version: r4478
* Operating system: W10
* Web browser: FF

### Step 2: Describe the problem:

error lines in the debug.log:

> INFO - Libsecpk256k1 loaded: FFILibrary_U:\ZeroNet-win-dist-win64\lib\coincurve\libsecp256k1.dll in 0.859s
> ERROR - Unhandled exception: AttributeError: module 'main' has no attribute 'file_server' in greenlet.py line 766 > Chart/ChartCollector.py line 171 > 29
> ERROR - Unhandled exception: AttributeError: 'Config' object has no attribute 'optional_limit' in greenlet.py line 766 > core/src/util/helper.py line 234 > OptionalManager/ContentDbPlugin.py line 362 > 325
> INFO - Version: 0.7.1 r4478, Python 3.7.3 (v3.7.3:..., Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)], Gevent: 1.4.0

Start by reproducing the two exceptions from debug.log and inspect greenlet.py line 766, then trace the reported callers in Chart/ChartCollector.py line 171, core/src/util/helper.py line 234, and OptionalManager/ContentDbPlugin.py line 362. Done means both AttributeErrors are understood and no longer occur in the reported ZeroNet environment, with regression coverage where appropriate.

索引モデルが issue の本文から書いたものです。