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.

config/locales/sk.yml

@@ -337,9 +337,7 @@ sk:
       reported_by: Nahlásené užívateľom
       resolved: Vyriešené
       resolved_msg: Hlásenie úspešne vyriešené!
-      silence_account: Zamĺčať účet
       status: Stav
-      suspend_account: Pozastaviť účet
       title: Reporty
       unassign: Odobrať
       unresolved: Nevyriešené