Extract middleware with UI to separate repository

[alebabai]

This repository is a part of large go-swagger project and acts as a runtime component for the generated code.
It follows from this that it carries with it many dependencies and other things.
But some simple http middleware with embed UI could be used out of scope of this package and generated code.

So, it would be nice to extract such middleware like SwaggerUI and Redoc to some separate repository, e.g. ui.

[deborggraever]

I like this idea. I'm using the UI middleware without generated code and would like to contribute some improvements.