Response messages in route config

I started using hapi-swagger (and it's great by the way) but one thing I disliked was the errors messages. I think this kind of configuration should stay in a hapi-swagger config option, so this does it. It's a breaking change but I think it's cleaner to do it this way than to support both and just confuse the users.

If this PR is approved let me know that i'll edit the readme.

Thanks!