Allow "now playing" submission for scrobble plugins
Both the audio scrobbler (last.fm) and ListenBrainz APIs support submitting "now playing" information, where the song currently listened to can be submitted and will be displayed. This is independent of the actual scrobble submission, that indicates that the track in question was actually listened to.
Provide a plugin hook that plugins can implement and that gets called when the user starts listening to a track.