Merge branch 'feature/group-level-labels' into 'master'

Add group level labels

## What does this MR do?

Add group level labels.

## Are there points in the code the reviewer needs to double check?

* `LabelsFinder`
* `Gitlab::Gfm::ReferenceRewriter`
* `Banzai::Filter::LabelReferenceFilter`

## Why was this MR needed?

We'll be adding more feature that allow you to do cross-project management of issues.

## Screenshots (if relevant)

* Group Labels
    ![Group Labels](/uploads/2244c06ad68eae4fb246fb4c81bf8060/2.png)

* Project Labels
    ![Project Labels](/uploads/c5839516d2282b51f7418d9dadbeceb4/1.png)

* Expanded references for group labels when moving issue to another project
    ![Expanded references for group labels when moving issue to another project](/uploads/0c9ab248a8420d4978d59349ae3d42e5/3.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [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
  - [ ] All builds are passing
- [ ] 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)
- [ ] 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)

## What are the relevant issue numbers?

#19997

See merge request !6425

1 files changed, 4 insertions, 5 deletions

diff --git a/app/views/shared/issuable/_filter.html.haml b/app/views/shared/issuable/_filter.html.haml
index 6b43a76c404..ed93857e6d4 100644
--- a/app/views/shared/issuable/_filter.html.haml
+++ b/app/views/shared/issuable/_filter.html.haml
@@ -78,11 +78,10 @@
           = hidden_field_tag :state_event, params[:state_event]
           .filter-item.inline
             = button_tag "Update #{type.to_s.humanize(capitalize: false)}", class: "btn update_selected_issues btn-save"
-
-  - if !@labels.nil?
-    .row-content-block.second-block.filtered-labels{ class: ("hidden" if !@labels.any?) }
-      - if @labels.any?
-        = render "shared/labels_row", labels: @labels
+  - has_labels = @labels && @labels.any?
+  .row-content-block.second-block.filtered-labels{ class: ("hidden" unless has_labels) }
+    - if has_labels
+      = render 'shared/labels_row', labels: @labels
 
 :javascript
   new UsersSelect();