Swagger UI & JSON URL

This PR adds two new options:

* Specify the URL where the swagger UI interface will be accessed [/swagger, /docs] etc.
* Specify the URL for the explorable JSON [/api-docs.json, /docs.json] etc.

This PR also removes code which was modifying the discovery URL within swaggers UI. This doesn't work with the latest swagger UI and IMO shouldn't be done like this anyways since people can just build that UI from source very easily.

Can you try it out and tell me what you think?