Fixes #671 (closed)
Fixes #696 (closed)
CSVs now have "external:SomeIdentifier" instead of a netid if a user does not have a netid.
Project ID,Assignment Naam,Gebruiker Name,Gebruiker NetID,Rol
54,internshsip one,David Alderliesten,dalderliesten,student
54,internshsip one,Maurício Aniche,maniche,Supervisor
54,internshsip one,Grzegorz Brzęczyszczykiewicz (Unregistered),external::GrzegorzBrzczyszczykiewiczUnregistered,Supervisor
54,internshsip one,Test Company1,external::Test Company1,offerer