Feature request: terms of use for new user

[schuettloeffel-elsa]

When using the admin frontend for more than a few admins (e.g. lecturers that upload videos directly from the admin ui), there has to be a way to supply a terms of use form on first login. The displayed text should off course be configurable and the user would have to accept the terms to continue.

Frontend issue: opencast/opencast-admin-interface#296