gbe-442: user and groups management (backend)

Server side code for adding possibility to save users and group information.
Shouldn't LoginSession be an extension of Authentication ? In Geomajas security, authentication gives you a key and an authentication object with all your authorizations. For deskmanager, first authorisation could be the authorisation to choose your profile. Then, after choosing the profile, you get the authorizations belonging to that profile. Makes sense ?