Add Asian Network and World Service streams
Log if playlist for station not found
Song Avoider using NowPlaying messages

When the "avoid" button is pressed, the currently playing song's
duration is used to determine when the avoiding should end.
Refactor to make stream request when station is played

Intriduces RadioStation class encapsulating stream logic. HTTP
requests are made only when station.playlist is requested resulting
in fewer HTTP requests
Better logging for now playing message in client
Use one-shot timer for avoiding
Auto-refresh radio streams before their expiry times
Expire Now Playing songs using duration
Ignore duplicate now playing messages
Avoider -> TrackAvoider
Label Track Avoider and cancel avoiding on channel change
Use proper BBC IDs rather than guessing
More robust expiry of now playing info (set expired flag and let clients decide what to do)
Remove unused files