title: jstree remove default elements from context menu
body: <p>I have a problem with JsTree's contextmenu, how can I remove the default elements from the contextmenu like Create, Delete, Rename? I want to provide elements of my own, but the default elements are still at the contextmenu. </p>
  
  <pre><code>    "contextmenu" : {
                      "items" : {
                          "IsimVer" : {
                              "label" : "İsim Değiştir",
                              "action" : function (obj) { this.rename(obj); }
                          },
                          "Ekle" : {
                              "label" : "Ekle",
                              "action" : function (obj) { this.create(obj); }
                          },
                          "Sil" : {
                              "label" : "Sil",
                              "action" : function (obj) { this.remove(obj); }
                          }
  }
  </code></pre>