Adds class to all sprites.
@param {String} cls CSS class name
function(obj) {
        var i = 0,
            items = this.items,
            surface = this.getSurface(),
            len = this.length;
        
        if (surface) {
            for (; i < len; i++) {
                surface.addCls(items[i], obj);
            }
        }
    }