Add the possibility to retrieve the current user groups

- groups are available in a UserData class containing also the user name.
- Added getCurrentUserData method in Scheduler and ResourceManager interfaces
- added logins/sessionid/{sessionId}/userdata rest call in Scheduler and RM rest interfaces
- added currentuserdata rest call in studio interface
- added tests in AuthenticationTest and SchedulerClientTest which checks that the UserData can be retrieved.