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

Conflicts:
- README.md
- app/helpers/statuses_helper.rb
  Upstream moved account helpers to their own file, we had extra
  helpers there, moved too.
- app/lib/sanitize_config.rb
- app/models/user.rb
- app/serializers/initial_state_serializer.rb
- config/locales/simple_form.en.yml
- spec/lib/sanitize_config_spec.rb

app/javascript/mastodon/locales/defaultMessages.json

@@ -776,6 +776,10 @@
       {
         "defaultMessage": "Unmute sound",
         "id": "video.unmute"
+      },
+      {
+        "defaultMessage": "Download file",
+        "id": "video.download"
       }
     ],
     "path": "app/javascript/mastodon/features/audio/index.json"