[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: Ie6e0f428a00c6e7eb7b3fd47bd9b4f85e0e2131e
Conflicts:
	core/java/android/provider/Settings.java
Conflicts:
	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java

Conflicts:
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java