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/views/layouts/public.html.haml

@@ -7,9 +7,9 @@
             = image_tag asset_pack_path('logo_full.svg'), alt: 'Mastodon'
 
           - if Setting.profile_directory
-            = link_to t('directories.directory'), explore_path, class: 'nav-link'
-          = link_to t('about.about_this'), about_more_path, class: 'nav-link'
-          = link_to t('about.apps'), 'https://joinmastodon.org/apps', class: 'nav-link'
+            = link_to t('directories.directory'), explore_path, class: 'nav-link optional'
+          = link_to t('about.about_this'), about_more_path, class: 'nav-link optional'
+          = link_to t('about.apps'), 'https://joinmastodon.org/apps', class: 'nav-link optional'
         .nav-center
         .nav-right
           - if user_signed_in?