Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- .github/ISSUE_TEMPLATE/bug_report.md
  Took our version.
- CONTRIBUTING.md
  Updated the embedded copy of upstream's version.
- README.md
  Took our version.
- app/policies/status_policy.rb
  Not a real conflict, took code from both.
- app/views/layouts/embedded.html.haml
  Added upstream's changes (dns-prefetch) and fixed
  `%body.embed`
- app/views/settings/preferences/show.html.haml
  Reverted some of upstream changes, as we have a
  page dedicated for flavours and skins.
- config/initializers/content_security_policy.rb
  Kept our version of the CSP.
- config/initializers/doorkeeper.rb
  Not a real conflict, took code from both.

app/serializers/rest/status_serializer.rb

@@ -37,6 +37,17 @@ class REST::StatusSerializer < ActiveModel::Serializer
     !current_user.nil?
   end
 
+  def visibility
+    # This visibility is masked behind "private"
+    # to avoid API changes because there are no
+    # UX differences
+    if object.limited_visibility?
+      'private'
+    else
+      object.visibility
+    end
+  end
+
   def uri
     OStatus::TagManager.instance.uri_for(object)
   end
@@ -97,7 +108,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   end
 
   def ordered_mentions
-    object.mentions.to_a.sort_by(&:id)
+    object.active_mentions.to_a.sort_by(&:id)
   end
 
   class ApplicationSerializer < ActiveModel::Serializer