Remove extraneous .gitkeep
Introduce email subscription workflow

Introduce the basic workflow for creating a new govuk_delivery topic and passing the user onto a subscription page on govuk_delivery.
Disallow external requests in specs
Make common API stubbing to specs

In order to use the same API stubbing between both specs and cucumber features, we will abstract the common code into the specs/support directory. These are included back into our features file so the code can be shared between both.
Spec email alert redirection at controller level

We cannot test external redirects with cucumber easily so instead lets spec this out at the controller level.
Specs for EmailAlertSubscriber

Looking at the specs it would be nice to separate out the EmailAlertSubscriber into 2 smaller classes which this class wraps. My suggestion would be GovUkDeliveryTopicCreator and GovUkDeliveryTopicFinder. These could then be injected into the EmailAlertSubscriber and both respond to a call method and would provide a simpler interface for testing.