Allow AniDB as an agent for movies

[Musi13]

This PR adds an AniDBMovieProvider class that allows anime to be included in Movie type libraries. Internally, it proxies all lookups to the existing Series provider.

Screenshots

[dkanada]

Are movies and shows treated the same on AniDB?

[Musi13]

Yes, on AniDB movies are just shows with one episode. Occasionally, there's a few more "episodes" for when a movie may be split into multiple parts, but that's the general rule.

Here's an example: https://anidb.net/anime/28#Episodes

[Musi13]

I think I've addressed your comments. The AniDbMovieImageProvider class was just copied from the existing AniDbSeasonImageProvider class, so I didn't look at formatting.

I've reworded the summary to be a bit more clear, and changed some of the methods to more directly call the SeriesImageProvider counterparts.

[Musi13]

I also have some changes to fix/improve searching (i.e. fix #50 and add images to search results). I thought I would make another PR after this is merged since those changes are unrelated, but that would mean revving the version twice.

Is that okay, or should I add them here so everything goes in as 5.0.0?

[dkanada]

I would revert the version bump in this one and we can merge it soon, then bump the version in your next pull request.

[Musi13]

Alright, I've removed the version bump from this PR and added it to a new branch. I can't PR that yet because it depends on the ImageProvider class in this one. But once this is in, I'll open the other PR.

[dkanada]

Thanks!