Frameworks: simplify custom lockscreen background code

- remove observer for transparency and handle it better
- add multisuser handles
- smaller fixes and code cleanup
- simpfliy custom background handling and change to our needs (thanks Danish)

Conflicts:
	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardHostView.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardViewBase.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardViewManager.java

patchset 2:
    set background color back to an int

Change-Id: Idf0bbb7bf9e132a3a68d567e3863cce1b6d99742