Improve button/keyboard backlight code.

- Improve UX
- Deduplicate code

Change-Id: Ie0218de8b83fe49e3fe1d91a64c2522af03ba06d

Conflicts:
	res/values-da/cm_strings.xml
	res/values-el/cm_strings.xml
	res/values-es/cm_strings.xml
	res/values-hu/cm_strings.xml
	res/values-it/cm_strings.xml
	res/values-ja/cm_strings.xml
	res/values-pt/cm_strings.xml
	res/values-ru/cm_strings.xml
	res/values/cm_strings.xml
	res/xml/button_settings.xml
	src/com/carbon/settings/fragments/ButtonBacklightBrightness.java
	src/com/carbon/settings/fragments/ButtonSettings.java
	src/com/carbon/settings/fragments/KeyboardBacklightBrightness.java