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'.