Merge branch 'issue_18575' into 'master'

Improve usability for prioritized labels

## What does this MR do?
- Adds an icon next to prioritized label rows serving as a hint to the user that the labels can be sorted by dragging them.
- Adds description about prioritized labels.
- Restores empty message when removing all prioritized labels.

## Screenshots (if relevant)

![labels](/uploads/1da16c4c54a894fa45ccc47e3a5bdf7a/labels.gif)

Closes #18575 

See merge request !4652

1 files changed, 5 insertions, 2 deletions

diff --git a/app/assets/javascripts/LabelManager.js.coffee b/app/assets/javascripts/LabelManager.js.coffee
index 365a062bb81..b06bcf0fcbf 100644
--- a/app/assets/javascripts/LabelManager.js.coffee
+++ b/app/assets/javascripts/LabelManager.js.coffee
@@ -42,10 +42,10 @@ class @LabelManager
       $from = @prioritizedLabels
 
     if $from.find('li').length is 1
-      $from.find('.empty-message').show()
+      $from.find('.empty-message').removeClass('hidden')
 
     if not $target.find('li').length
-      $target.find('.empty-message').hide()
+      $target.find('.empty-message').addClass('hidden')
 
     $label.detach().appendTo($target)
 
@@ -54,6 +54,9 @@ class @LabelManager
 
     if action is 'remove'
       xhr = $.ajax url: url, type: 'DELETE'
+
+      # Restore empty message
+      $from.find('.empty-message').removeClass('hidden') unless $from.find('li').length
     else
       xhr = @savePrioritySort($label, action)