Implement Android 5.0 notification color and public version

Notifications in Android 5.0 can have a background color over the small icon and can specify a separate public and private version (where potentially sensitive details can be hidden from the public version). This implements both features, using a blue grey color matching the system apps' notification color and hiding the image and the artwork title from the public version.
Merge pull request #80 from ianhanniballake/notification_v21

Implement Android 5.0 notification color and public version