The manager now sets a cookie when playing a track, and retrieves it
when loading the playlist, to start where the user left off.
using cookie-js.
The manager is not responsible for knowing if a new Track playing is
in the radio playlist, or somewhere else. It's the current controller
that decides if it plays radio tracks or not (default behaviour is
that it's a radio track).
Incidentally, the radio manager doesn't fire Radio:newTrackPlaying
events, it's the current controller that does (it feels weird though).
The manager now sets a cookie when playing a track, and retrieves it when loading the playlist, to start where the user left off.