Parsing cleanup

The new parsing code was a bit confusing to me, so I started going in and cleaning it up a bit. Changes so far:
- Series parsers now take name parameter optionally, and automatically guess series name when none is supplied.
- Stripped out a lot of stuff from the two parser plugin classes. Just leave the parse_movie and parse_series methods
- Both series parsers now just override with passed in quality if it is passed in
- Unit tests were running the guessit and internal subclasses as well as base class in many cases

TODO:
- [ ] ~~I'd like to make the data structures that guessit uses for its results a bit more pythony and strip out the stuff we aren't using~~ Delaying this bit for a future pull.


@Toilal Let me know what you think. Some of this stuff was confusing to me, let me know if I break any intended functionality.