Port "Bind VolUp+VolDown to toggle the ringer"

Squash of http://review.cyanogenmod.org/#/c/20256/ and
http://review.cyanogenmod.org/#/c/22716/

Change-Id: Ied3767969482a7ea44f7f0e9222a2f78fe8f507c
Merge "Port "Bind VolUp+VolDown to toggle the ringer"" into kk4.4