Add method to PowerManager that allows querying the lowest possible
brightness.

Used by the auto-brightness adjustment to adjust the sliders.

Change-Id: Idb58fd86dee1a053fe858291be6c9b3169ac4247
Lockscreen Targets: Icon Revamp

Adjust the size of custom app icons and resize and round the corners
of gallery icons for a more uniform look.

Before http://imgur.com/cTOqdwX

After http://imgur.com/EKAeFiw

Change-Id: Ibcca275eb0ae946775773a8c8217b6508da10e5b