[1/2] Base: Lockscreen blur

Show the content behind lockscreen, blurred.

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

Change-Id: I0d7ee20d6b415567f0051d716ba0db2e55511e91

Conflicts:
	core/java/android/provider/Settings.java
	services/java/com/android/server/power/DisplayPowerController.java