Fixed some Prototypes from being globally defined

src/graph/Groups.js

@@ -2,10 +2,10 @@
  * @class Groups
  * This class can store groups and properties specific for groups.
  */
-Groups = function () {
+function Groups() {
   this.clear();
   this.defaultIndex = 0;
-};
+}
 
 
 /**

src/graph/Images.js

@@ -2,11 +2,11 @@
  * @class Images
  * This class loads images and keeps them stored.
  */
-Images = function () {
+function Images() {
   this.images = {};
 
   this.callback = undefined;
-};
+}
 
 /**
  * Set an onload callback function. This will be called each time an image

src/timeline/TimeStep.js

@@ -24,7 +24,7 @@
  * @param {Date} [end]           The end date
  * @param {Number} [minimumStep] Optional. Minimum step size in milliseconds
  */
-TimeStep = function(start, end, minimumStep) {
+function TimeStep(start, end, minimumStep) {
   // variables
   this.current = new Date();
   this._start = new Date();
@@ -36,7 +36,7 @@ TimeStep = function(start, end, minimumStep) {
 
   // initialize the range
   this.setRange(start, end, minimumStep);
-};
+}
 
 /// enum scale
 TimeStep.SCALE = {