Support new vibrate/silent behavior.

The updated settings tree looks like this:

	[ ] Silent mode (unchanged)
	[ ] Allow vibration in silent mode (new)
		Phone vibrate: (changed from boolean)
		( ) Always
		( ) Only in silent mode
		( ) Never

See change I14cf91b0 for explanation & framework support.

Change-Id: I22ba7bcfa5ddf4e545800083c6e80fb655f211e5