SystemUI: Added Notification Sound Toggle to PowerWidget (1/2)

The power widget this patch adds effectively toggles ONLY the notification sounds.
Typically when you silence or force-vibrate your phone, it does this to both ringer+notification sounds.
This behaviour is by design in Android since 2.2.

What this toggle does is switch between notification sound volume 0 and whatever you have set,
not "muting" it by Android standards (since you can't w/o also muting ringer), but still silencing it.

For people who want to be able to quickly silence notifications but still hear the ringer.

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Patchset 2: Added mdhi graphics

Change-Id: I51e4e53ff0592dac5e57a10fc745578e7b69918e
Merge "SystemUI: Added Notification Sound Toggle to PowerWidget (1/2)" into jb4.2