Add player state to r4-app.config

[oskarrough]

check what we do in r4 ember.

maybe r4-app.state.{playlist,currentTrack,isPlaying}

so we can:

locate current channel and current track (from navigating to url) display them as active in UI everywhere they're displayed

[oskarrough]

On r4-app we have

isPlaying, playingChannel, playingTrack

seems good.