[2/2] OmniGears: SeekBarPreferences tweaks

-added @string support for units
-use SeekBarPreference for button brightness timeout

Change-Id: Iec10dd13ab7eb1f974b8a850fbbd39d897a7e0cc

Conflicts:
	res/layout/seek_bar_preference.xml
	res/values/custom_attrs.xml
	res/values/custom_strings.xml
	res/xml/brightness_settings.xml
	src/org/omnirom/omnigears/brightness/BrightnessSettings.java
	src/org/omnirom/omnigears/chameleonos/SeekBarPreference.java