groups: port missing functionality

* Implement user group manage function

* Add filter on list of group that user can join.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
The values in the select are linked with the group selected.
I didn't find how to pass the `id_usergroup` to the `QuerySelectField()`'s constructor, so I "manually" fill the values.
Can I pass the parameter "id_usergroup" to the `UserJoinGroupForm` form?