An extension point for stylesheets

Hey Richie,

To continue the discussion we've had in https://github.com/domaindrivendev/Swashbuckle/pull/4
First of all, thanks for your work and even bigger thanks for your response speed. You've saved me a bunch of work-hours pointing out things that could be found in documentation if I was to read it carefully. Here I've tried the approach you suggested about injecting stylesheets, and it works like a charm. Please take a look when you get a chance and tell whether this is what you've expected or maybe some things need to be changed. I mean, it works for me, but I only know my use cases, maybe there are some underwater stones in a bigger perspective.

Another thing is that this addition won't work until you add a line '%(EmbeddedStylesheet)' to index.html of swagger-ui, and that one is a - what - embedded solution? I'm new to this stuff and I'm not sure how to handle it, I guess I'll have to post a pull request to the swagger-ui repository? Would this work?

Thanks

Alex