Comments: Further range of content reference ux improvements

- Added reference indicator to comment create form.
  - Added remove action.
- Extracted reference text to translations.
- Changed reference hash to be text-based instead of HTML based.
- Added reference display for newly added comments.
- Handled reference marker delete on comment delete.

resources/sass/_components.scss

@@ -569,6 +569,9 @@ body.flexbox-support #entity-selector-wrap .popup-body .form-group {
   border-bottom: 0;
   padding: 0 vars.$xs;
 }
+.tab-container [role="tabpanel"].no-outline:focus {
+  outline: none;
+}
 
 .image-picker .none {
   display: none;