Feature/json resource

Make it possible to fo a GET that returns handler info as JSON. It is conceptually similar to the debug request in that it does not make a subsequent upstream call. The motivation is that an application can make a call to the deviceproxy service outside the request-response loop.
I'd prefer doing a new numbered release, document the breaking backwards compatibility and add this as a normal positional argument. This kind of stuff is going to make maintenance super messy over time.