Normalize add/remove to support multiple args
Normalize add/remove to support multiple args

For browsers that natively support classList, normalizes add/remove to
always support adding or removing multiple classes at a time. Affects
Firefox < 26 and IE 10/11.

gitkiselev/classList.js,sergeikriger/classList.js,sergeikriger/classList.js,sergeikriger/classList.js,mospired/classList.js,yola/classlist-polyfill,mospired/classList.js,yola/classlist-polyfill,eligrey/classList.js,lynzz/classList.js,gitkiselev/classList.js,eligrey/classList.js,gitkiselev/classList.js,yola/classlist-polyfill,lynzz/classList.js,lynzz/classList.js,mospired/classList.js,eligrey/classList.js