Add a middleware to support running the swagger-editor.

[delaneyj]

Per a conversation with @whitlockjc on IRC it would be great to have the swagger-editor.

I had mocked up taking the exisiting 2.0 example and injecting the editor parts. It seems like the swagger-node editor launcher is doing some shared config setup throughout so cleaning this up and making an real middleware like the validator/ui would be awesome.