Add a format to Video and use it for matching

I used the feedback from Wackou from guessit (wackou/guessit#86) and used the GuessProperties to search for the format.
I've implemented the format on Episode and Movie level.
Unit tests have been adapted accordingly.
Please review and give feedback.

PS: I didn't know what to pick for the score for the format, so please adapt if needed (current equation: format = video_codec + audio_codec).