Keyguard: add smart cover support

Signed-off-by: Roman Birg <roman@cyngn.com>

Conflicts:
	packages/Keyguard/res/values/cm_strings.xml
	packages/Keyguard/src/com/android/keyguard/KeyguardViewManager.java
	packages/Keyguard/src/com/android/keyguard/KeyguardViewMediator.java

bring back parts from:
https://github.com/CyanogenMod/android_frameworks_base/commit/99193055525db039b651fc8c88678b6e6e74efc9
removed by:
https://github.com/CarbonDev/android_frameworks_base/commit/135989074ca13cb9a47c478620634d676688272c

Change-Id: I436eba7678b923a9f293e15d786447214bc9bdcb