Feature/exhaustive overview

This MR merges the exhaustive overview into master; the overview is a reviewer-only element, which displays the entire state of the ongoing correction (all students, labels, submissions, comments etc.). There are also tests for the overview, but they fail on remote (due to memory issues). They do work reliably on local however.

Note: the branch also contains a lot of changes to the functional_tests/, making them more reliable and consistent.