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.
Yeah, it does. It's a quick extraction of existing logic to test a nested health page approach. I've not rewritten the health probes properly yet, but this logic will be going away :)