Store babel languages in the database
The current method of reading categories and parsing languages out of
them is a terrible hack, and a TODO comment suggests to use a database,
which is a much better structured storage format.
This adds a babel database table, which if $wgBabelUseDatabase is
true, will be used to store the languages a user knows, and at what
Once the database is populated and created everywhere, we should remove
the fallback category code.