set nickname if a member is created

fet2020/authentications/authentications.py

@@ -58,6 +58,7 @@ def authentication(username, password):
         member.firstname = firstname
         member.surname = surname
         member.username = username
+        member.nickname = username
         member.mailaccount = mail
         logger.info(f"Member '{username}' created.")
         member.save()