function isScrollable(el) {
      var isScrollableY = hasScrollableSpace(el, 'Y') && canOverflow(el, 'Y');
      var isScrollableX = hasScrollableSpace(el, 'X') && canOverflow(el, 'X');

      return isScrollableY || isScrollableX;
    }
indicates if an element can be scrolled in either axis
@method isScrollable
@param {Node} el
@param {String} axis
@returns {Boolean}