* Do not raise unretryable exceptions in ResolveRemoteAccountService

* Removed fatal exceptions from ResolveRemoteAccountService

Exceptions that cannot be retried should not be raised. New exception
class for those that can be retried (Mastodon::UnexpectedResponseError)

* Add specs for unsubscribe service

* Fix non existent methods in unsubscribe service

* Clean up status handling in subscribe service

* Dont use raise_error by itself (avoids warning)

* Add coverage for AccountFilter

* Improve coverage and refactor for Subscription#lease_seconds

* Improve coverage and refactor for NotificationMailer

* Simplify assignment of min/max threshold on subscription

* 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