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/initializers/sidekiq.rb

@@ -19,4 +19,4 @@ Sidekiq.configure_client do |config|
   config.redis = redis_params
 end
 
-Sidekiq::Logging.logger.level = ::Logger.const_get(ENV.fetch('RAILS_LOG_LEVEL', 'info').upcase.to_s)
+Sidekiq.logger.level = ::Logger.const_get(ENV.fetch('RAILS_LOG_LEVEL', 'info').upcase.to_s)