Feedback history bypasses subscriptions

Summary

A user can change his feedback via the feedback history while another tutor is currently validating it.

Steps to reproduce

Log in two tutors, create feedback and get into validation stage. The other tutor can still edit his previously created feedback

What is the expected correct behavior?

The tutor should not be able to edit feedback where another one has a subscription to. On the other hand, tutors should not get a subscription to submissions that are being edited via the feedback history.

added Bug Needs assignment labels

this is a duplicate of #155 (closed)

closed