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/views/admin/domain_blocks/new.html.haml

@@ -14,5 +14,8 @@
   .fields-group
     = f.input :reject_media, as: :boolean, wrapper: :with_label, label: I18n.t('admin.domain_blocks.reject_media'), hint: I18n.t('admin.domain_blocks.reject_media_hint')
 
+  .fields-group
+    = f.input :reject_reports, as: :boolean, wrapper: :with_label, label: I18n.t('admin.domain_blocks.reject_reports'), hint: I18n.t('admin.domain_blocks.reject_reports_hint')
+
   .actions
     = f.button :button, t('.create'), type: :submit