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/initializers/doorkeeper.rb

@@ -59,6 +59,7 @@ Doorkeeper.configure do
                   :'write:accounts',
                   :'write:blocks',
                   :'write:bookmarks',
+                  :'write:conversations',
                   :'write:favourites',
                   :'write:filters',
                   :'write:follows',
@@ -78,7 +79,6 @@ Doorkeeper.configure do
                   :'read:lists',
                   :'read:mutes',
                   :'read:notifications',
-                  :'read:reports',
                   :'read:search',
                   :'read:statuses',
                   :follow,