User registration on Cuddlers CMS

User registration on the Cuddlers CMS after user has followed the states:registration:* leg of the customer journey.
So what if I set the user's state to the previous state and come to this state via an `.input`? It will essentially be a duplication of what I do [there](https://github.com/praekelt/vumi-go-cuddlers/blob/feature/issue-1-user-registration-on-cuddlers-cms/test/app.test.js#L555) (but I'll be testing for the `reply` as opposed to the `state` in `.check.interaction`).

I like the fact that I test the navigation to a state and its content in two separate tests, so if at all possible I'd want to keep it that way.

Thoughts?