Keep track of users who have viewed a changeset (BB-6132)

It would be nice to know who has read a changeset. We use peer reviewing a lot, and require that at least 2 developers (other than the committer) read every changeset. Right now, it is impossible to tell if anyone has looked at a change set unless there is a comment or it has been improved. Our rule is that you only approve if you do not find fault, otherwise you comment. In order for us to tell f the 2 dev rule has been met, the second dev has to add a "me too" if they have no further comments...

Perhaps adding the dev or user as a participant with an eye icon (like the approve checkmark icon) if they have read but not commented or approved? This would also help scrum masters identify if people are actually taking part in the review process.