Add .hgignore.
Make a few user-facing and db changes.

Start listings at index 1.
Add season_episode_number to database.
Finish poller.py. Make some db schema changes. Fix enqueue.py.

Poller is now complete.
The episodes table now contains a gid field for use with aria2 download id.
Enqueue wasn't adding the tvshow when adding episodes earlier. Fixed now.