Approve and unapprove quick actions

I'm not sure there's a lot more to say, it would be cool to be able to submit /approve instead of clicking the Approve button (so 2016!).

Quick actions for approve and unapproving a merge request.
/Approve [italic]Approve this merge request[/italic]
/Unapprove [italic]Unapprove this merge request[/italic]
Ddetect all the conditions of approvability/unapprovability when the merge request loads, and thus, make the quick action unavailable. I.e. only provide the quick action for /approve only if the current user can approve. Same for /unapprove.

Edited Mar 29, 2018 by Victor Wu