WIP: Group MR numbers on issue show page by project and namespace

Open username-removed-235897 requested to merge brunsa2/gitlab-ce:26466-natural-sort-mrs into master

What does this MR do?

Groups MRs on the issue show page into those for the current project, those for projects in the namespace, and projects outside of the namespace. This makes the ordering consistent with the work done on #7110.

Are there points in the code the reviewer needs to double check?

None that I can think of. Maybe if anything, a visual separator between different projects?

Why was this MR needed?

Consistency with other ordering.

Screenshots (if relevant)

Old: Screen_Shot_2017-01-08_at_4.56.14_PM New: Screen_Shot_2017-01-08_at_4.52.12_PM

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #26466 (moved)