Add default settings for user (#4393)

config/settings.yml

@@ -17,9 +17,11 @@ defaults: &defaults
   closed_registrations_message: ''
   open_deletion: true
   timeline_preview: true
+  default_sensitive: false
+  unfollow_modal: false
   boost_modal: false
-  auto_play_gif: false
   delete_modal: true
+  auto_play_gif: false
   system_font_ui: false
   noindex: false
   notification_emails: