Implement directed hard/soft dependencies on top of relations
While https://gitlab.com/gitlab-org/gitlab-ce/issues/4058 led to relations, these are not enough to model, and automatically visualize, dependencies. https://gitlab.com/gitlab-org/gitlab-ce/issues/29171 had been created, but closed due to a timing overlap with closing https://gitlab.com/gitlab-org/gitlab-ce/issues/4058 .
I am not sure how much actual rationale is needed as the issue is borderline obvious:
Issues sometimes depend on each other in a hard or soft way, a hard dependency preventing closing of the depending issue before all dependencies are closed. Once relations are upgraded to an actual concept of dependencies, it's easy to create a directed graph along with issue states from the issue tracker.