Add support for multiple class names in utils add/remove class methods. (#3079)

* Add support for multiple class names in utils add/remove class methods.
Reset subgroup heights in resetSubgroups method.

* Adjust to better process class names

lib/timeline/component/Group.js

@@ -534,6 +534,7 @@ Group.prototype.resetSubgroups = function() {
   for (var subgroup in this.subgroups) {
     if (this.subgroups.hasOwnProperty(subgroup)) {
       this.subgroups[subgroup].visible = false;
+      this.subgroups[subgroup].height = 0;
     }
   }
 };

lib/util.js

@@ -621,12 +621,13 @@ exports.getAbsoluteTop = function (elem) {
  * @param {Element} elem
  * @param {String} className
  */
-exports.addClassName = function (elem, className) {
+exports.addClassName = function (elem, classNames) {
   var classes = elem.className.split(' ');
-  if (classes.indexOf(className) == -1) {
-    classes.push(className); // add the class to the array
-    elem.className = classes.join(' ');
-  }
+  var newClasses = classNames.split(' ');
+  classes = classes.concat(newClasses.filter(function(className) {
+    return classes.indexOf(className) < 0;
+  }));
+  elem.className = classes.join(' ');
 };
 
 /**
@@ -634,13 +635,13 @@ exports.addClassName = function (elem, className) {
  * @param {Element} elem
  * @param {String} className
  */
-exports.removeClassName = function (elem, className) {
+exports.removeClassName = function (elem, classNames) {
   var classes = elem.className.split(' ');
-  var index = classes.indexOf(className);
-  if (index != -1) {
-    classes.splice(index, 1); // remove the class from the array
-    elem.className = classes.join(' ');
-  }
+  var oldClasses = classNames.split(' ');
+  classes = classes.filter(function(className) {
+    return oldClasses.indexOf(className) < 0;
+  });
+  elem.className = classes.join(' ');
 };
 
 /**