Light settings: reduce tone if preview image color is very light

Prevents material whiteout in color preview.

Change-Id: Idfa47e57bdb669b17b610b737d0fe2c942b47d78
Settings: add double-tap to sleep in Advanced Settings

Adapted for cm-12.0

Conflicts:
	res/values/cm_strings.xml
	res/xml/display_settings.xml
	res/xml/status_bar.xml

Change-Id: I910eb6624536b437d0bf14f64c1eeacafaa59cfa