updated constructors for timeline and graph2d (container, items, groups, options) with backwards compatibility

lib/timeline/Graph2d.js

@@ -18,7 +18,14 @@ var LineGraph = require('./component/LineGraph');
  * @constructor
  * @extends Core
  */
-function Graph2d (container, items, options, groups) {
+function Graph2d (container, items, groups, options) {
+  // if the third element is options, the forth is groups (optionally);
+  if (!(groups instanceof Array || groups instanceof vis.DataSet) && groups instanceof Object) {
+    var forthArgument = options;
+    options = groups;
+    groups = forthArgument;
+  }
+
   var me = this;
   this.defaultOptions = {
     start: null,

lib/timeline/Timeline.js

@@ -18,11 +18,18 @@ var ItemSet = require('./component/ItemSet');
  * @constructor
  * @extends Core
  */
-function Timeline (container, items, options) {
+function Timeline (container, items, groups, options) {
   if (!(this instanceof Timeline)) {
     throw new SyntaxError('Constructor must be called with the new operator');
   }
 
+  // if the third element is options, the forth is groups (optionally);
+  if (!(groups instanceof Array || groups instanceof vis.DataSet) && groups instanceof Object) {
+    var forthArgument = options;
+    options = groups;
+    groups = forthArgument;
+  }
+
   var me = this;
   this.defaultOptions = {
     start: null,
@@ -92,6 +99,11 @@ function Timeline (container, items, options) {
     this.setOptions(options);
   }
 
+  // IMPORTANT: THIS HAPPENS BEFORE SET ITEMS!
+  if (groups) {
+    this.setGroups(groups);
+  }
+
   // create itemset
   if (items) {
     this.setItems(items);