Update brightness slider code from aokp

and fix a race condition in the event handling

Squashed commit of the following:

commit b2fb70e86a410c49abe9d058fe61fd3dbafd7ca8
Author: Roman Birg <romanbirg@gmail.com>
Date:   Thu Nov 22 14:03:58 2012 -0600

    SystemUI: re-implement statusbar brightness slider

    Change-Id: I96db3d8f40adf3726f4140c3ad3a7122e0ad6add
    Signed-off-by: Roman Birg <romanbirg@gmail.com>

commit 3ce32b8ab061406ded11090adfb7c6f780a718ca
Author: nuclearmistake <nuclearmistake@gmail.com>
Date:   Sat Dec 21 12:20:49 2013 -0500

    Revert "systemui: add brightness slider 2/2"

    This reverts commit 34233ec666fc91c15e9755d493eb6cf1e49b0ced.

Change-Id: Id12a55f2a93cec9553509b9ff6c35d898264cec4