Add PowerManager integration for button and keyboard backlight.

Allows setting button and keyboard backlight brightness as well as
button timeout.

Change-Id: I550cccafc0a8f90d6347de9261adb26b75955cc4

Conflicts:
	core/java/android/os/PowerManager.java
	core/java/android/provider/Settings.java
	services/core/java/com/android/server/power/PowerManagerService.java
SystemUI: Add missing import

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
SystemUI: Add dummy path for stat_sys_signal_none

Change-Id: I0e459002d84aef3f7ddc21134dc56d215de16a51
SystemUI: Re-adjust signal strength icons

Change-Id: Id6dad0800e5e15ec694b24ecb9a88ccc0d4771d8
Enhance power menu reboot option

* Use our old reboot icon
* Set correct dialog title & message when rebooting
* Move strings to cm_strings
* Add back reboot_download string used by samsung devices
* Remove Chinese translations, will be handled through crowdin

Change-Id: I3ba0e20dcdba0a295a071304048eebab6cfcf49d