Notification sound field updates

- Show default and silent options
- Don't also update the default notification sound
- Display a better summary in case the sound isn't in media store

Change-Id: I42d537657a7bbddb8a1ce41fd03b8e5847899a82
Fixes: 36734113
Fixes: 36849670
Test: manual (silent sound, default sound, normal sound, private sound)