Revert "Remove 'Allow custom buttons' checkbox (2/2)"

This reverts commit 45a662d0b29f02f3695cc75e3df25e3e38546a54.

	modified:   res/values-ca/cm_strings.xml
	modified:   res/values-de/cm_strings.xml
	modified:   res/values-es/cm_strings.xml
	modified:   res/values-it/cm_strings.xml
	modified:   res/values-lt/cm_strings.xml
	modified:   res/values-nl/cm_strings.xml
	modified:   res/values-pl/cm_strings.xml
	modified:   res/values-pt/cm_strings.xml
	modified:   res/values-ru/cm_strings.xml
	modified:   res/values-th/cm_strings.xml
	modified:   res/values/cm_strings.xml
	modified:   res/xml/button_settings.xml
	modified:   src/com/android/settings/cyanogenmod/ButtonSettings.java