(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.
I think seconds is probably granular enough, I don't think we need to go down to millis.  I'd also probably suggest including the unit in the setting name (e.g. shutdown-timeout-seconds) so that it's very clear.  Lastly, I think we talked through the shutdown stuff with Haus and decided on 60s as the default?