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/javascript/flavours/vanilla/theme.yml

@@ -7,7 +7,7 @@ pack:
     filename: common.js
     stylesheet: true
   embed: public.js
-  error:
+  error: error.js
   home:
     filename: application.js
     preload: