Add Screen Off option for buttons double-tap/long press (2 of 2)

Depends on I7e0c21b174b9cdd020c8d27c91c4c72201e228ff (c/69163)

This is being done primarily to replicate functionality on find7 Color OS.
Would it be better/possible to have this change only affect the find7?
(Updated to address string concerns)

Change-Id: I6f0c07b6e6c7834194cbb766cd425850ba7df324