radio stations in playlists

1) radio stations could be able to be added to the end of a playlist. So at the end of a list if podcasts, a specified stream starts playing.

2) the alarm, when set to a radio station, overrides the playlist if it's playing. I think currently the alarm just doesn't work if there's a podcast playing.

3) an “exact time marker” in a playlist. At the specified time, the playlist advances to the maker and plays the subsequent item, which could be a podcast or radio station.