[Interfaces] Reworked IRadioStationProvider to work with abstract models.

This breaks the build.
[HotStreams] Ported to new-style interface.
[LMP] Ported to new IRadioStationsProvider interface.

I'm so glad Util::MergeModel becamse so powerful with the introduction of
abstract ModelItem. That's what I call composability!

The build is still broken, though.
[TS] Ported to new IRadioStationProvider interface.