Mbst 8930 refactor radioplayer

First version of this, it's still WIP. I'm looking for thoughts on how to reduce the complexity, particularly around the InteractionManager, as this class is doing most of the complicated interactions between queue and file records.
I *think* this is now fixed. There's a few error cases which I hadn't fully fleshed out, they should hopefully be better now, as I spent a while trying to test all of the edge cases.