Finish implementing Firma hinzufügen, and added-by-student functionality that will be overriden whenever an admin does any change to the student-entered firmen. Also did some cosmetic modifications to the firmen list and excluded all student-entered firmen from view whenever the user is not an admin. The student may now also enter kontaktdaten for the firmen they create, which should make up for the fact that they cannot edit the firmen they have entered and thus cannot add kontakten later.