Undomanager and ctrl+z/ctrl+y

@ryandeba I tried and now undo and redo button does not do anything(not even blank editor canvas) I have below code
`[{
      id: "undo",
      className: "fa fa-undo icon-undo",
      command: function command(editor, sender) {
        sender.set("active", 0);
        editor.UndoManager.undo(1);        
      },
      attributes: {
        title: "Undo (CTRL/CMD + Z)"
      }
    }, {
      id: "redo",
      className: "fa fa-repeat icon-redo",
      command: function command(editor, sender) {
        sender.set("active", 0);
        editor.UndoManager.redo(1);
      },
      attributes: {
        title: "Redo (CTRL/CMD + Y)"
      }
    }`