GitLab Special refs
Part of heptapod#431 (closed), closes #48 (closed) and does the special refs part of #50 (closed)
All legacy (hg-git based) Projects have been automatically migrated to native with the upgrade of 2025-01-23
Part of heptapod#431 (closed), closes #48 (closed) and does the special refs part of #50 (closed)