Todos sorting dropdown Implements #18135 ![todos_sorting](/uploads/bff76827c421628134dfb8b864e47c74/todos_sorting.png) - [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added - Tests - [x] Added for this feature/bug - [x] All builds are passing - [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 you do - rebase it please) - [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits) See merge request !5691