[1/2] Base: Hide power menu on lockscreen

Adds an option to enable/disable power menu on lockscreen.

Settings: https://gerrit.omnirom.org/#/c/4702/

Change-Id: I0de1501d0ecedb7b9b08fbb3aebaecd0e63cc09e
Merge "[1/2] Base: Hide power menu on lockscreen" into android-4.4