Port to Python3

[janpascal]

Python2 is end-of-life, so fix all compatibility issues with Python3.
Some of the dependencies may make this problematic: twistar for Python3 may not have complete Python3 support.

As an alternative, the denyhosts sync server could be rewritten completely using the now standardized Python3 asyncio, aiohttp, aiohttp-xmlrpc and an asyncio ORM like tortoise-orm, but that would require some serious development effort

[josev814]

Can we get a branch of python_27 specifically for the current version. That way if users need to use python 2.7 they can switch to that branch.

Then we can focus master or another branch on getting updated to python 3.x

[josev814]

Looking over aiohttp vs Flask I was seeing that aiohttp is faster than Flask by 3x.
One interesting bit was when using aiohttp with gunicorn, it allowed aiohttp and Flask to serve requests even faster. Should gunicorn be looked at as part of the aiohttp impementation?

https://stackabuse.com/asynchronous-vs-synchronous-python-performance-analysis/