Add persistent notification with play/pause/stop buttons

Creates additional buttons for play, pause, and stop in the notification. 

Options for: 
 - Keep notification when paused.
 - Auto expand the notification.

Addresses #405 except for lock screen.
The top notification is always expanded by default, so if the AP notification is not at the top, it requires the user to manually expand it. Setting the priority high causes the AP notification to always be at the top, and therefore always be expanded.