SystemUI: Port forward statusbar brightness control

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

Change-Id: Icc04e7da3286e9925f8b90528c1e022b33d33e9d
SystemUI: fix status bar brightness slider eating events

In some cases it would eat the event and not lose focus to the rest of
the system.

Change-Id: I94d532d09ea762edf7ac037043ed023caf42c401
Signed-off-by: Roman Birg <roman@cyngn.com>