Emby Support

[Schaka]

This serves a milestone to keep track of Emby support.

The decision to support Emby was made, because it remains very similar to Jellyfin and it should be possible to support both while not running both myself.

Requirements before publishing to main:

• [x] Implement Authorization via API key and user
• [x] Validate whether media deletion works without user and make user optional
• [x] Implement Leaving Soon collection via file system access
• [x] Implement REST DELETE for movies
• [x] Implement REST DELETE for tv shows
• [x] Unify and deduplicate code between Emby/Jellyfin services
• [x] Validate whether REST services between the two need to be different or can be interfaced
• [x] Simplify enabling one or the other
• [x] Adjust docs to reflect that Emby is low priority or find Emby maintainer

[Schaka]

@hacshacdgacs this is available in the develop build and will be published in a few days in version 1.0 of Janitorr.