Improve merge request discussion flow

Proposal

At present when opening a merge request and there are a large number of on-going discussions it is difficult to quickly filter through the ones that require your attention.

Presently it is only possible to view all unresolved threads. It lacks filtering options such as viewing resolved threads or thread that specifically require the current users attention or where they were not the last user to comment in the thread.

Also if a reviewer has commented on the merge request and the merge requestor has addressed the concern, they can only close the discussion and no pass it back to the original commenter to approve/acknowledge this. This means that the original comment wont be aware of the progress of the discussion.

Therefore the proposal is to improve the ability to pass action items between reviewer and merge requestor to implement changes and review those changes or continue the discussion.

And for open discussions to be filterable to action items relevant to the user logged in.