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.

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