add a users and active_users relation to the group model
add a users and active_users relation to the group model

This is used to join all useres or active users in a query

Signed-off-by: Jan Losinski <577c4104c61edf9f052c616c0c23e67bef4a9955@wh2.tu-dresden.de>

lukasjuhrich/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft