UI subtitles support

[KiraLT]

In the UI player, it would be useful to have the ability to select subtitles.

Features

• [ ] Allow selecting subtitles from the current torrent
• [ ] Allow adding subtitles from local file
• [ ] Allow adding subtitles from remote file (enter URL)
• [ ] Opensubtitles support and new API endpoint
• [ ] Allow selecting subtitles in the UI player from Opensubtitles:
  • [ ] Ability to search
  • [ ] Automatically find by IMDB id