tvdb_id and imdb_id must be unique.
Improved admins sites for Episode and Series to easu usage.
Merge remote-tracking branch 'upstream/master' into unique-id-tvdb_id
Merge remote-tracking branch 'upstream/master' into unique-id-tvdb_id
Merge pull request #29 from nessita/unique-id-tvdb_id

Add unique constraint tvdb_id and imdb_id.