'Add the given group to this service.
@type group: L{IGroup}
@rtype: L{twisted.internet.defer.Deferred}
@return: A Deferred which fires with L{None} when the group is
added, or which fails with
L{twisted.words.ewords.DuplicateGroup} if a group with the
same name exists already.'

def addGroup(self, group):

    raise NotImplementedError
