Add nested groups support to the routing ## What does this MR do? It allows routing with `/` in namespace name ## Why was this MR needed? For nested groups feature(https://gitlab.com/gitlab-org/gitlab-ce/issues/2772). We need URI like `/group/subgroup/project` be routed correctly ## Does this MR meet the acceptance criteria? - [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added - ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~ - ~~API support added~~ - Tests - [x] Added for this feature/bug - [x] All builds are passing - [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html) - [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides) - [x] Branch has no merge conflicts with `master` (if it does - rebase it please) - [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits) ## What are the relevant issue numbers? https://gitlab.com/gitlab-org/gitlab-ce/issues/2772 See merge request !7459
