change port in jetty runner

todo: externalize to settings file
dummy download controller

decodes url but returns nothing useful
reduce logging
implement download for request and response

TODO: name is not pretty
TODO: ignore-case for headers
add download links on exchange page
preserve case for headers

this produces possible inconsistent behaviour
when a server produces multiple headers with
the same name but different capitalization,
but the risk of that is lower than problems
caused by clients that assume headers are case-sensitive.