Re-add lockscreen music controls toggle.

Change-Id: I70fb6c0d20caad7af01a45b4a9374eb107a554a3

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

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