make link to merge request visible from commit
say you have merge request: !4839 (merged), it has one commit: https://gitlab.com/gitlab-org/gitlab-ce/commit/a6faaace0503c27884808740e002c201b8893375
currently there's no way to navigate back to merge request from commit from gitlab web ui. please add such support
it helps navigating back to merge request to get more context of the commit in question