This is a draft PR for the shuffle feature. I'll keep working on this and ask for reviews along the way to make sure I don't drift off too far.

I've been thinking about a smart way of implementing this and will open up another ticket with my design idea soon.

For now this contains:

• Added a shuffle button to AuxControls
• Mirroring the data flow of other UI components, playbackmanager passes any state updates to the playbackengine

Next TODO:

• Add base shuffle functionality for playback queue in playbackengine