- Added an update reason to the abstraction, for the episode/series
  update events.

- Refactored the AnimeCreator to track most changes to the anime object,
  including changes to the title, episodes, and tags. We can optionally
  also track changes to the characters/staff, but I left it out for now.

- Hooked up the AnimeCreator to emit added/updated/removed events
  for anidb episodes.

- Updated the GetAniDBAnimeJob to also emit added/updated events
  for anidb anime (series).

- Added a server model for the anidb episode, and rewired the IEpisode
  in the plugin abstraction to use this new model instead of the shoko
  episode model. This is to align the models in the abstraction, making
  it easier to add IShoko\* entries later that the metadata is tied to,
  without having the shoko models implementing both the shoko interface
  and the metadata interface for anidb.

- This commit **MAY** break plugins, but since I didn't edit any
  existing interfaces or classes related to renaming then I think it
  will be fine.