item: modernize tracking graph editor

- set validator, this is now required to be able to edit
- use an iframe for ERP5JS compatibility

bt5/erp5_item/SkinTemplateItem/portal_skins/erp5_item/Item_viewTrackingList/my_jsplumb_graph.xml

@@ -233,7 +233,7 @@
                 </item>
                 <item>
                     <key> <string>gadget_url</string> </key>
-                    <value> <string>dream_graph_editor/jsplumb/index.html</string> </value>
+                    <value> <string>gadget_graph_editor.html</string> </value>
                 </item>
                 <item>
                     <key> <string>hidden</string> </key>
@@ -241,7 +241,7 @@
                 </item>
                 <item>
                     <key> <string>js_sandbox</string> </key>
-                    <value> <string></string> </value>
+                    <value> <string>iframe</string> </value>
                 </item>
                 <item>
                     <key> <string>renderjs_extra</string> </key>