Add transparency settings for lockscreen (1/2)

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

Change-Id: I8c15d0afbbdd442167faf0bc9eaeaf76ed2dea9d
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>

Conflicts:
	res/values/strings.xml