code: def connect_callbacks(self, callbacks_bag):
          
          notconnected = []
          for wname, builderobj in self.objects.items():
              missing = builderobj.connect_commands(callbacks_bag)
              if missing is not None:
                  notconnected.extend(missing)
              missing = builderobj.connect_bindings(callbacks_bag)
              if missing is not None:
                  notconnected.extend(missing)
          if notconnected:
              notconnected = list(set(notconnected))
              msg = 'Missing callbacks for commands: {}'.format(notconnected)
              logger.warning(msg)
              return notconnected
          else:
              return None
docs: Connect callbacks specified in callbacks_bag with callbacks
          defined in the ui definition.
          Return a list with the name of the callbacks not connected.