[4/4] find5: custom brightness support

-enable button brightness support
-change liblights to support separate button setting
-cleanup sensor settings

PS3:
using a value of 0 for config_screenBrightnessSettingMinimum is not
a good idea :)

Change-Id: Id888d55427d1d79de2be23621d8d9e47013dca55
Merge "[4/4] find5: custom brightness support" into android-4.3