Allow group pages / collections to be submitted / locked

When students work together in project groups and create a page / collection collaboratively, they may have to submit that page / collection for assessment to a group - either the same or another group where the students are members of.

Thus, it would be good if group pages could also be submitted for assessment.

(idea from http://myportfolio.school.nz/interaction/forum/topic.php?id=7355 - not accessible publicly; just for Kristina's reference)