Disable the tabbed panel until the user clicks on a node

In order to prevent the situation when a user clicks on 'add note' after
reseting the database without having created a node (which breaks) we now
start with the right-hand side tab panel disabled.

This commit closes #16

public/javascripts/interface.js

@@ -25,6 +25,7 @@ var dradistabs = new Ext.TabPanel({
   activeTab: 0,
   border: false,
   deferredRender: false,
+  disabled: true,
   //margins: '0 5 0 0',
   items: [
     notesbrowser,