LockScreen: add option to minimize challenge when showing the lockscreen (1/2)

This will allow the user to choose wether the lockscreen
challenge (circle, pattern, pin) is minimized when the screen
is turned on.

PS2: rebase
PS3: hide if needed after inflation

Change-Id: Ib5bd0a84e5542a49d34ed8c8541e10a7878a616c
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>

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