code: def is_empty(self):
          
          if super(Group, self).is_empty():
              return True
          for child in self.children:
              if not child.is_empty():
                  return False
          return True
docs: A group of modules is considered empty if it has no children or if
          all its children are empty.
  
          >>> from admin_tools.dashboard.modules import DashboardModule, LinkList
          >>> mod = Group()
          >>> mod.is_empty()
          True
          >>> mod.children.append(DashboardModule())
          >>> mod.is_empty()
          True
          >>> mod.children.append(LinkList('links', children=[
          ...    {'title': 'example1', 'url': 'http://example.com'},
          ...    {'title': 'example2', 'url': 'http://example.com'},
          ... ]))
          >>> mod.is_empty()
          False