RadioPlayer fixes for BBC stations

`radioplayer.js` currenty assumes that all stations put "Artist - Track" in the marquee at the top of the player, but BBC stations have had their own "Now Playing" box for a while and don't use the same place.

This PR checks for the BBC stations usual `div` and checks in the correct place for those stations, keeping the current behaviour for other stations.

Happy to make any changes if you feel I've left anything out or not done something correctly.