Fix issue with diff comments path

At the moment this just fixes the JS and view stuff related to refactoring file-path-

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7814 for more details.

• Changelog entry added
• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

Related: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7814