Merge branch 'issue-boards' into 'master'

Issue boards

- Issue: #17907
- Issue backend: #20335
- Backend MR: !5548
- Frontend MR: !5554
- Documentation !5713

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [X] ~~API support 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)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5548

app/views/shared/issuable/_filter.html.haml

@@ -27,7 +27,9 @@
           = render "shared/issuable/label_dropdown"
 
         .pull-right
-          - if controller.controller_name == 'boards' && can?(current_user, :admin_list, @project)
+          - if controller.controller_name != 'boards'
+            = render 'shared/sort_dropdown'
+          - if can?(current_user, :admin_list, @project)
             .dropdown
               %button.btn.btn-create.js-new-board-list{ type: "button", data: { toggle: "dropdown", labels: labels_filter_path, project_id: @project.try(:id) } }
                 Create new list
@@ -36,8 +38,6 @@
                 - if can?(current_user, :admin_label, @project)
                   = render partial: "shared/issuable/label_page_create"
                 = dropdown_loading
-          - else
-            = render 'shared/sort_dropdown'
 
     - if controller.controller_name == 'issues'
       .issues_bulk_update.hide