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/views/about/show.html.haml

@@ -38,7 +38,7 @@
                 %small= t('about.browse_public_posts')
 
         .directory__tag
-          = link_to 'https://joinmastodon.org/apps', target: '_blank', rel: 'noopener' do
+          = link_to 'https://joinmastodon.org/apps', target: '_blank', rel: 'noopener noreferrer' do
             %h4
               = fa_icon 'tablet fw'
               = t('about.get_apps')