* Fix#2473 - Use sidekiq scheduler to refresh PuSH subscriptions instead of cron
Fix an issue where / in domain would raise exception in TagManager#normalize_domain
PuSH subscriptions refresh done in a round-robin way to avoid hammering a single
server's hub in sequence. Correct handling of failures/retries through Sidekiq (see
also #2613). Optimize Account#with_followers scope. Also, since subscriptions
are now delegated to Sidekiq jobs, an uncaught exception will not stop the entire
refreshing operation halfway through
Fix#2702 - Correct user agent header on outgoing http requests
* Add test for SubscribeService
* Extract #expiring_accounts into method
* Make mastodon:push:refresh no-op
* Queues are now defined in sidekiq.yml
* Queues are now in sidekiq.yml
