Auto-expand a discussion note when we arrive via anchor
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4575#note_12361432 is a link to a note on an outdated diff. We should auto-expand that note's containing block when arriving via a link, and maybe scroll to it as well, so that it's obvious where the note is. Right now you have to toggle every single collapsed discussion div until you find the right one.
cc @DouweM