Statusbar Brightness Control (AOKP impl) (1/2)

Find it more effective than CM...

re-implement statusbar brightness slider

TODO: allow it to be disabled by adding a System.Setting?

Signed-off-by: Roman Birg <romanbirg@gmail.com>

SystemUI: add statusbar slider preference

Change-Id: Ibad11cd0495aa5fc2aa31e6f6c1e1cf85b8a582b
Signed-off-by: Roman Birg <romanbirg@gmail.com>