Highlight updated merge requests

Description

Developers tend to re-click through merge requests where nothing happened.

Proposal

An indicator in the list of open merge requests that shows that a merge request was updated (by commits or discussions) since the developer's last visit.

Documentation blurb

1. Looking at the list of merge requests, developers don't know which merge requests changed since their last visit.
2. Remember when a developer checks a merge request. If there's an updated version of a merge request, when the developer loads the list of merge requests, show the updated one with an additional symbol after the title. (For example a filled cirlce, probably an empty one for the other merge requests as well)
3. Now, the developer can see which merge request might be interesting and which won't - without checking e-mail notifications or checking all the merge requests.