Lockscreen: Add back lockscreen wallpaper (1/2)

Much simper implementation than in previous releases.

PS2: Rebase + small AOSP formatting fixes
PS3: Remove abstract from void.
PS5: Rebase for 4.3

Change-Id: Id67bc9fc6613c9d978354556191456e1141344b9

Conflicts:
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardViewBase.java