Implement missing audio_service features and drop using the fork

[nt4f04uNd]

There are multiple features that are a non-trivial time investment to implement and get the author of the library to review and merge them, because they invlove writing and testing the code for multiple platforms, and both me and the author have other stuff to do.

From the top of my head, those are the most imporant ones:

• Default album art ryanheise/audio_service#666
• Fallback image for media items with missing arts ryanheise/audio_service#309
• support more actions in media notification ryanheise/audio_service#633

The entire diff between the fork and the latest audio_service version can be seen here https://github.com/ryanheise/audio_service/compare/minor...nt4f04uNd:audio_service:sweyer?expand=1

Using the fork prevents us from getting the latest changes from the library and will eventually become so stale, I will either have to cherry-pick new changes into it, or be forced to implement those features.