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/helpers/application_helper.rb

@@ -84,7 +84,7 @@ module ApplicationHelper
   end
 
   def cdn_host
-    ENV['CDN_HOST'].presence
+    Rails.configuration.action_controller.asset_host
   end
 
   def cdn_host?
@@ -92,10 +92,10 @@ module ApplicationHelper
   end
 
   def storage_host
-    ENV['S3_ALIAS_HOST'].presence || ENV['S3_CLOUDFRONT_HOST'].presence
+    "https://#{ENV['S3_ALIAS_HOST'].presence || ENV['S3_CLOUDFRONT_HOST']}"
   end
 
   def storage_host?
-    storage_host.present?
+    ENV['S3_ALIAS_HOST'].present? || ENV['S3_CLOUDFRONT_HOST'].present?
   end
 end