Settings: Fix "Use actual storage type of sdcard/usb (1/2)."

Fixes http://review.cyanogenmod.org/63744

The original patch used the same string ids for sd in both cm_strings.xml and strings.xml.
Change them so there isn't a clash causing the wrong strings to be displayed by always prefixing the aosp ids with either sd_ or usb_.

Change-Id: Iad509123a9b4b93677b6ec06f15c34d9b0f57165

Conflicts:
	res/values/cm_strings.xml
cm_colors.xml -> custom_colors.xml

Change-Id: Ia12e5ea72d7b2f1256814dff6e27974efe9d709d