title: change node icon using fancytree.js
body: <p>I am using fancytree.js for treeview and I have a callback on the tree:</p>
  
  <pre><code>$("#tree").fancytree({ 
      source: {url: "/" + appPath + "/pathosadmin?treepages=true"},
      postProcess: function (event, data) {
          data.result = convertData(data.response, true);
      },
      init: function (event, data) {
          var root = $("#tree").fancytree("getRootNode");
          root.sortChildren(function (a, b) {
              return treeSort(a, b);
          }, true);
      },
      icon: function (event, data) {
  
          switch (data.node.data.NODE_TYPE) {
              case 1: //page
                  if (data.node.data.STARTPAGE == 0) {
                      return "fancytree_page_icon";
                  } else if (data.node.data.STARTPAGE == 1) {
                      _this.startPageNode = data.node;
                      return "fancytree_startpage_icon";
                  }
              case 2: //group
                  return "fancytree_group_icon";
              case 3: //level
                  if (data.node.data.LEVELID) {
                      switch (data.node.data.LEVELID) {
                          case 1:
                              return "fancytree_level_1_icon";
                          case 2:
                              return "fancytree_level_2_icon";
                          case 3:
                              return "fancytree_level_3_icon";
                          case 4:
                              return "fancytree_level_4_icon";
                          case 5:
                              return "fancytree_level_5_icon";
                      }
                  } else {
                      return "fancytree_location_icon";
                  }
          }
      },
      extensions:
  </code></pre>
  
  <p>Now I want to also change the icons on runtime. Sadly </p>
  
  <pre><code>if (_this.startPageNode) {
       _this.startPageNode.icon = "fancytree_page_icon";
       _this.startPageNode.renderTitle();
   }
   activeNode.icon = "fancytree_startpage_icon";
   activeNode.render();
   _this.startPageNode = activeNode;
  </code></pre>
  
  <p>doesnt work. Any hints on how to tackle that problem. The node.icon attribute is always undefined and even if i set it (+render the node) it doesnt show. </p>