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

Conflicts:
- `README.md`:
  Our README.md files are completely different. Discarded upstream changes.
- `app/javascript/core/admin.js`:
  Updating rails-ujs, no real conflict, but a comment to close to changed
  code. Various glitch-soc-only files have been updated to match those changes,
  though.
- `package.json`:
  No real conflict, just an additional dependency in glitch-soc that was too
  close to something updated upstream. Took upstream's changes.

config/locales/ja.yml

@@ -565,7 +565,6 @@ ja:
     warning_presets:
       add_new: 追加
       delete: 削除
-      edit: 編集
       edit_preset: プリセット警告文を編集
       title: プリセット警告文を管理
   admin_mailer: