Visible items bug (#2878)

* Fix redraw order

* Fix error when option is not defined

* Allow template labels

* Add .travis.yml file

* Add experiment travis code

* Fix react example

* Fix getVisibleItems method

* Remove console log

lib/timeline/component/ItemSet.js

@@ -546,7 +546,7 @@ ItemSet.prototype.getVisibleItems = function() {
   for (var groupId in this.groups) {
     if (this.groups.hasOwnProperty(groupId)) {
       var group = this.groups[groupId];
-      var rawVisibleItems = group.visibleItems;
+      var rawVisibleItems = group.isVisible ? group.visibleItems : [];
 
       // filter the "raw" set with visibleItems into a set which is really
       // visible by pixels