Notification vibration improvements: [DO NOT MERGE]

 - When notifications vibrate as a fallback (that is,
   because they want to play a sound but the device is in
   vibrate mode), this no longer requires the VIBRATE
   permission.
 - As a bonus, if your notifications use DEFAULT_VIBRATE,
   you don't need the VIBRATE permission either.
 - If you specify a custom vibration pattern, you'll still
   need the VIBRATE permission for that.
 - Notifications vibrating in fallback mode use same
   vibration pattern but can be changed easily in future.
 - The DEFAULT_VIBRATE and fallback vibrate patterns are now
   specified in config.xml.

Bug: 7531442
Change-Id: I7a2d8413d1becc53b9d31f0d1abbc2acc3f650c6