It should not be possible to add a grader without a name

[Evgeny Kotelnikov]

The form for adding new graders to the course accepts plain email addresses without any names. In such cases it simply create a user account with empty first and last name, which occasionally leads to problems. Really, we should either require a name or ask the newly added grader for their name before completing the registration.

[Evgeny Kotelnikov]

Improve the grader addition form (fixes #132 #142)

→ <<cset f0e6372690c3>>