pep257 docstrings fixs for bot.py

Also:
- added pywikibot/__init__.py to tox.ini.
- sorted pep257 compatible files in tox.ini 'white-list'.

Change-Id: I3acd4b6a944cbef9f50375332895abf0d10d3f92
Merge "pep257 docstrings fixs for bot.py"