Group stats by show

* Split `data['games']` to `data['shows'][show]['games']` for each `show`.
* Fix (hopefully) every reference of `data['games']`.
* New commands: `!show` and `!show override ID`.
* There is a stats page for each show and for all shows.
* Votes page is segmented per show. Current game is is brought to the top along with other games played during that show.

Closes #33.