Support labeling Merge Request review discussions

Problem to solve

Every diff comment on a merge request is considered actionable (although it might be resolved). I want to be able to leave comments that aren't actionable, giving praise on lines of code that I think are great for example.

It'd be pretty neat if GitLab supported praising as a first class feature. Applications that natively promote positive communication lead to happy people.

Further details

(Relevant slack discussion)

I like to label my comments when I review MR's. What would it look like for GitLab to support parsing these labels?

Examples:

• nitpick: Typo. Change proyect to project.
• praise: Thanks for removing this code duplication! 👍
• suggestion: This code is fairly complex... I wrote a patch to make some of the existing logic simpler. WDYT?
• issue: There's a UX issue on Firefox. Here's a screenshot:

Crucible also supports categorization:

Defect	Explanation

Proposal

Given that not all diff comments are the same, it'd be nice for the following use cases to be met...

As a contributor, I'd like to know the severity of open discussions (i.e. 4 nitpicks is significantly different than 4 issues). 

As a frequent contributor, I'd like to review my *praise* comments if I'm having a bad day.

Links / references