Implement new volume display policy.

Whenever a stream type is muted, the progress bar in volume panel
is at 0.
If a stream is muted by ringer mode and does not control ringer mode,
the progress bar is disabled.
Pressing VOL- when in vibrate or silent mode resets the last audible
volume of ringtone stream (music strem on tablets) to 0.

VolumePanel implementation:
 - Always prefer AudioManager APIs over AudioService APIs when available on both.
 - Do not use AudioManager.shouldVibrate() (deprecated).

Change-Id: I57fcb19ada4e8d729b6b41d668496562ebe340c3