Add transparency settings for lockscreen (2/2)

This will enable the user to set the transparency level
for the lockscreen.

Change-Id: I624b2e136432bb0effceac9f7d41c78c65d22125
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>

Conflicts:
	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardViewBase.java
Revert "Lockscreen : Add custom background overlay"

This reverts commit fa583e172247cc4c863f53bf92ef71c65fe96ff1.

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