Add role() method to state object

Change-Id: Ie98f15c83d94c6cb1915942bba6c2ba17ae321e0
diff --git a/dev/js/src/buttongroup.js b/dev/js/src/buttongroup.js
index 65ea860..29453c3 100644
--- a/dev/js/src/buttongroup.js
+++ b/dev/js/src/buttongroup.js
@@ -106,12 +106,6 @@
      * Add button that can toggle a state.
      * The state has to be a state object.
      */
-    /*
-     * TODO:
-     *   Do not add a state object here, but embed the
-     *   state in the data and "roll()" through the different
-     *   state options instead.
-     */
     addToggle : function (title, data, state) {
       let b = this._element.addE('span');
       b.setAttribute('title',title);
@@ -147,11 +141,7 @@
         e.halt();
         
         // Toggle state
-        if (state.get()) {
-          state.set(false)
-        } else {
-          state.set(true);
-        }
+        state.roll();
       });
 
       return b;