SystemUI: attach a queue to media player notifications

Extend media player notificatoins to attach a queue below them, set via
the MediaController.setQueue() API, when available.

Long pressing on the notificaiton will reveal an option to disable the
queue.

The queue is currently hardcoded to be limited to 3 items.

Ticket: CYNGNOS-217
Change-Id: I3b8503cb47af2d36f031d06aefc1bfbe7ed80010
Signed-off-by: Roman Birg <roman@cyngn.com>