Change `manager` from `PAP.Person` to `PAP.Subject`
Add query attribute `my_group`

Unfortunately, at the moment, the query expression
`Q.my_group.member_links.left == person` doesn't work (see
_CNDB/_OMP/__test__/SAW_SQL.py for tests that show why).
Set `max_value` of `A_IP6_Netmask` to 128
`_Mixin` `CNDB.OMP.Entity` (tnx CT)