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

Conflicts:
- app/controllers/admin/base_controller.rb
  Some refactoring made upstream, no real conflict.
- app/javascript/mastodon/features/compose/components/compose_form.js
  Updated using upstream's code but using maxChars instead of the
  hardcoded length of 500 characters per toot.
- app/javascript/styles/mastodon/components.scss
  Upstream redesigned the onboarding modal. Not sure why we had a
  conflict there.

app/javascript/mastodon/locales/en.json

@@ -228,6 +228,14 @@
   "notification.reblog": "{name} boosted your status",
   "notifications.clear": "Clear notifications",
   "notifications.clear_confirmation": "Are you sure you want to permanently clear all your notifications?",
+  "notifications.filter.all": "All",
+  "notifications.filter.mentions": "Mentions",
+  "notifications.filter.favourites": "Favourites",
+  "notifications.filter.boosts": "Boosts",
+  "notifications.filter.follows": "Follows",
+  "notifications.column_settings.filter_bar.category": "Quick filter bar",
+  "notifications.column_settings.filter_bar.show": "Show",
+  "notifications.column_settings.filter_bar.advanced": "Display all categories",
   "notifications.column_settings.alert": "Desktop notifications",
   "notifications.column_settings.favourite": "Favourites:",
   "notifications.column_settings.follow": "New followers:",