(TK-92) Add graceful-shutdown support

Add graceful-shutdown support to the Jetty9 Webservice. Now,
when the webserver is shutdown, the server will give open
requests a chance to resolve themselves. Allow user to
configure the graceful shutdown stop timeout.
depending on the answer to the "zero" question, this could maybe be simplified to

`(.setStopTimeout s (or shutdown-timeout default-graceful-stop-timeout))`