Replace the TestRunner APIs with HttpServer and ProxyServer.
Fix filters.
We don't need a namespace for a single class.
Add Handler.ConfigureRequest() in preparation to split this into client- and server-part.
Finally remove Handler.CreateRequest().
Make HttpClientRequest public.
Add TraditionalRequest.SendAsync() to run it async.
We only need the async version of this method.
NTLM somehow got lost here; put it back.