code: function setValidationClasses(element, success) {
    var add = (success ? 'validate-positive' : 'validate-negative');
    var remove = (success ? 'validate-negative' : 'validate-positive');
    if (element.className.indexOf(add) < 0) {
      $(element).removeClass(remove).addClass(add);
    }
  }
docs: classes are only changed if not set right now
  
  @param {Element} element HTML DOM element to change validation classes
  @param {boolean} success true if positive validation class shall be assigned, false for error class