Media Player improvements

Suggestion:
Add the following to the media player of Nextcloud:

- Shuffle
- Repeat
- Next file automatically played (suggested in https://github.com/nextcloud/android/issues/12534 already), so a playlist consisting of media (audio/video) has to be created and non-media files in a folder are excluded automatically from such a list.
- Media Player Notification controls when app is minimised

A good example can be found in the HiDrive application.