Added empty class on empty filter groups.
Added empty class on empty filter groups.

bobsilverberg/moztrap,shinglyu/moztrap,shinglyu/moztrap,mozilla/moztrap,mccarrmb/moztrap,mozilla/moztrap,mozilla/moztrap,shinglyu/moztrap,mccarrmb/moztrap,shinglyu/moztrap,shinglyu/moztrap,bobsilverberg/moztrap,mccarrmb/moztrap,mozilla/moztrap,mccarrmb/moztrap,mccarrmb/moztrap,mozilla/moztrap,bobsilverberg/moztrap,bobsilverberg/moztrap