Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- app/controllers/directories_controller.rb
- app/controllers/settings/applications_controller.rb
- app/controllers/settings/base_controller.rb
- app/controllers/settings/deletes_controller.rb
- app/controllers/settings/exports_controller.rb
- app/controllers/settings/follower_domains_controller.rb
- app/controllers/settings/imports_controller.rb
- app/controllers/settings/migrations_controller.rb
- app/controllers/settings/notifications_controller.rb
- app/controllers/settings/preferences_controller.rb
- app/controllers/settings/sessions_controller.rb
- app/controllers/settings/two_factor_authentication/confirmations_controller.rb
- app/controllers/settings/two_factor_authentication/recovery_codes_controller.rb
- app/controllers/settings/two_factor_authentications_controller.rb

Conflicts were due to some refactoring already made in glitch-soc
when introducing flavours.

db/migrate/20181207011115_downcase_custom_emoji_domains.rb

@@ -0,0 +1,7 @@
+class DowncaseCustomEmojiDomains < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    CustomEmoji.in_batches.update_all('domain = lower(domain)')
+  end
+end