Updated to use the updated FileActions API

- removes the call to .display() (note: https://github.com/owncloud/core/pull/9254 needs to be merged first)
- updated to use OCA.Files.fileActions

@MorrisJobke for some reason I'm unable to test this. It seems the sound manager never sets itself up, so the calls to FileActions.register() never happen.

I thought the FileActions.register() call should happen earlier ? Or does it need the music player to somehow init itself in the background ?