The field holds the name of the grading evaluation method recently used
for the workshop or the default one to be used. At the moment there are
no alternatives but 'best' plugin. But I want to have the field there
before 2.0 stable release and also want to include it in workshop
backups.
If a user is allowed to allocate a submission to herself for assessment,
there is now a button that she can press to immediately allocate and
assess the submission.
This patch also contains various cleanups spotted during the work.