Issue with Large Discussion Performance

Problem

Viewing an issue with a large amount of content often takes a long time, because they is so much of the content to load into the page when a user navigates to the issue. This is especially pronounced when the comment thread is very long, with a lot of content including large images.

Solution

These issues break the problem into smaller pieces, and should probably be solved in this order:

• https://gitlab.com/gitlab-org/gitlab-ce/issues/24591 View issue quickly by not loading everything
• https://gitlab.com/gitlab-org/gitlab-ce/issues/24592 View issue discussion thread quickly by loading in chunks
• https://gitlab.com/gitlab-org/gitlab-ce/issues/24593 View specific comment in an issue quickly

Previous remarks

We would like to make UX where the issue that is being loaded loads right away and all other discussions load via ajax. cc @awhildy @tauriedavis