Worker service

* Adds a service to the container which runs the sneakers worker
* Fix a TypeError in the rake task
`ActiveJob::Base.subclasses`.. calling this alone should be enough as `ActionMailer::DeliveryJob` inherits from `ActiveJob::Base`. The problem is that `ActionMailer::DeliveryJob` isn't eager loaded. So we could just reference it first to load it. We'll end up duping the class in the array with the current method.