add rest call to shut the server down, and a gui link (in the help page for now, until we find a better place)
fix groovy script so errors don't show previous data
improve REST API doc (Swagger) content: better, more consistent endpoint names, layout, and swallowing useless scary error messages;
also moved "/v1/version" to "/v1/server/version" (kept the old one, but deprecated)
do mgmt.terminate on ServerResource.shutdown