feat(dynamite): Support default responses

[provokateurin]

Closes #871

I had this laying around from the petstore example. Might as well merge it already now that we have tests for dynamite.

[Leptopoda]

How does this handle having both a status code and a default response specified?

I think we really have to make the status code validation taka a function that uses a switch case. This would also allow us to handle status code ranges.

[provokateurin]

It is handled the same way as we currently do for multiple status codes: As long as they have the same schema they will be handled the same. If we have a default response then we can ignore if we have other status codes with the same schema because they will be handled by the default already.
I don't think we need your function for this yet (although we certainly need it in the future for supporting multiple schemas). I would like to keep everything as simple as possible until we actually need something more complex.

[Leptopoda]

The please also add a test that handles this (having both a default and a status code)

[Leptopoda]

LGTM

[Leptopoda]

You'll need to rebase as I just merged #1025.