To make all bots consistent add shared function in bot_lib.py
to check if this bot is called. All bots respond to at-mention of
the bot instead of their specific names.
Incorrect Index access in wikipedia.py resulted in IndexError and
wikipedia bot to crash for few queries. This causes the bug to be fixed.
Replaced url to avoid 2 redirects and enhance performance.
Fixes: #3508.
In order to make the layout of all bots consistent, this commit
moves each bot into a folder with its name and modifies 'run.py'
so that only bots with such a structure can be executed. 'lib'
gets renamed to 'bots'.