MR Review: Resolve discussion, Edit and Delete comment

Problem to solve

Currently, users can only view comments on MRs. If they want to interact with these comments, they'll have to switch to the web interface.

Proposal

Implement resolving discussions, editing and deleting comments as described in detail in #269 (closed).

Resolving/unresolving discussions

Edit comment

Delete comment

Stretch: Open the comment in the browser

Further details

The "POC Result" section of the POC issue provides a detailed technical description of the features

Links / references