VolumeZen: Slider icon as ringer-mode toggle.

- When manipulating the ringer/notification stream, the volume
  slider icon on the left now serves as a toggle.  Single-press
  for vibrate, long-press for silent.
- Disable slider when silent.
- Add touch feedback to slider icon when clickable.
- Vibrate when toggling to vibrate.
- Play sound when toggling to audible.
- Adjust the slider icon padding so it appears to be square,
  and the same size as the icon on the right.

Bug:15330217
Change-Id: Id7262d9315e6e761e1d5750714c356c3ac735951