s/posixGroup/groupOfNames/g WIP
Improving error handling in ldapadmin

- catching of ldap errors more accurate
- better feedback in case of error in the angularJS UI

Note: this commit is mainly a feedback of runtime testing of the PR 575,
for now at account creation / deletion. More tests and commits to come.
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
removed fixmes
Merge pull request #575 from georchestra/groupofnames

s/posixGroup/groupOfNames/g