Students created via LDAP initially have no student number

Student numbers are unavailable via LDAP. Hence, when students are created via LDAP, they initially have no student numbers.

This may cause problems in some situations, such as:

1. A student's participation in a course is imported via their student number
2. The student is created via LDAP for a different reason
3. The student finally logs into ProjectForum via SSO. Their participation in the course is not assigned properly because when the user was created there was no student number to link it to.

There may also be other functionality affected by this behaviour.