Fixing LDAPAdmin

Going from posixGroup to groupOfNames requires a code revamp of the
webapp. The modifications proposed in this commit are far from perfect,
but allows to keep ldapadmin isofunctional.

Testing:
Done mainly manually.

TODO:
- some cleaning of the current code ;
- better approach to avoid hardcoded parameters and use more massively
  parameters from shared.maven.*
- adding some unit / integration tests