SystemUI : Port forward statusbar brightness control

Brings back the status bar brightness control from cm-10.2/cm-11

Change-Id: Icc04e7da3286e9925f8b90528c1e022b33d33e9d
SystemUI: improve brightness slider behavior

Mimic the brightness slider behavior in the statusbar.
This adds logic to make the statusbar slider also work with automatic
brightness mode enabled and it will instead adjust the temporary automatic
brightness overrride.

Change-Id: I78814a785decc83df94844fcc2f489c8cbec2b65
Signed-off-by: Roman Birg <roman@cyngn.com>