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

Conflicts:
- app/serializers/rest/instance_serializer.rb
- app/views/layouts/error.html.haml
- public/oops.png
  Took our version (same as upstream but without the things that only
  make sense in an animation).

Additional changes:
- app/javascript/flavours/vanilla/theme.yml
  Include upstream's javascript in error pages.

app/controllers/api/v1/apps/credentials_controller.rb

@@ -6,6 +6,6 @@ class Api::V1::Apps::CredentialsController < Api::BaseController
   respond_to :json
 
   def show
-    render json: doorkeeper_token.application, serializer: REST::StatusSerializer::ApplicationSerializer
+    render json: doorkeeper_token.application, serializer: REST::ApplicationSerializer, fields: %i(name website vapid_key)
   end
 end