Frameworks: customizable slim lockscreen background (1/2)

- color fill (with transparency slider)
- custom image (with transparency slider)
- full transparent
- default

Change-Id: I5506ebb11644d4c31e06380363f19967f9c958b8

	modified:   core/java/android/provider/Settings.java
	modified:   policy/src/com/android/internal/policy/impl/keyguard/KeyguardViewManager.java
	modified:   services/java/com/android/server/wm/WindowAnimator.java

Cherry-picking will cause all files to conflict

https://github.com/temasek/android_frameworks_base/commit/d1bb90a04e842b5c90dce46743de5fc6b441acf2