Extend backend by proxying API to swagger2openapi

[MikeRalphson]

Now that we have an npm module (thanks @yogendra) and potentially a docker container, maybe it makes sense to add swagger2openapi to the node_modules so conversions and validations can be done by the in-built webserver/backend without having to call out to and depend on apps deployed to heroku or appspot , which might not always be available.

Questions:

• How to avoid code duplication with openapi-webconverter?
• How to identify we have been served by the intelligent back-end and not by file:// or a simple server like github pages?

[MikeRalphson]

• file:// is easy to detect with window.location.protocol or similar.
• xhr.getAllResponseHeaders() on an AJAX call could detect a custom header.

Note: loading index.html from a file:// url is broken, at least on my Windows environment, so the README.md has been updated.

• Detection of the 'intelligent' backend is now done.
• Refactoring of openapi-webconverter pending this PR refactoring request parsing, fixing response format detection openapi-webconverter#3
• Switching of the converter url to be relative
• Testing.