Started work on music soruces

Signed-off-by: Simon Post <simon.post@cpw.co.uk>
Started work on music sources
Added transport icons
Added volume and mute control
Added better handling of the timing bar to lower network traffic
Made changes to the Spotify is handled to take account of the changes in the latest Sonos release where it now uses a Session ID not your Spotify userID
Plus a few tweaks elsewhere…..

Signed-off-by: Simon Post <simon.post@cpw.co.uk>