Tutors need access to Participantspage

Description / Overview

In Exercise-Mode, Tutors need access to a Participants-page that can filter Participants by Exercise-Group.

Use cases

Better Overview for Tutors.

Links / references

Feature checklist

• Add a Filter to Participants-page to filter by Exercise-group
• Grant Tutor permission to access the Participants-page when in Exercise-mode

(Make sure these are completed before closing the issue, with a link to the relevant commit.)