Include support for user Groups in LDAP

Description

This ticket is to track the changes in the LDAP userprovider to be compatible with Opencast user Groups.

The code has been tested during the last schoolyear in the University of Cologne's local version of Opencast. The pull request associated to this commit will be a port of that code to the 4.0 version.

Fixed and reviewed

Assignee

Rubén Pérez

Reporter

Rubén Pérez