debug mode for quizzes (and homeworks, ...)

[kohlhase]

It would be good if the TAs (or some suitable ACL) could actually take the quiz (for testing) outside the quiz times. Currently I get

event as a quiz admin.

But we had a problem with the quizzes today, where I had not realized that students cannot type in $\forall$ in the \fillinboxes
And I imagine that if I or one of the TAs has really taken the quiz to test it, then this would have been discovered.
All I had done was send the TAs the PDF, and that clearly was not sufficient.

I actually think that there should (eventually) be a whole third mode to the quiz: the "debug mode", where sufficiently authorized people can take the test and have a very easy way of making comments to the test author.