Adjust access to profil/update. Access should be allowed when there is no vertiefung set in the user's profile, and the user should be redirected to it in this case as well (done in AuswahlController). Also, if the student is BO studiengang, they should arrive at the profile page right after every login, but if they change the vertiefung during the session they shouldn't be allowed access to do so again (we use a flag for this). Also removed link to profil in auswahl, since the users should only get to the profile/update automatically now.