Return cherrypy.server to a single-server model
The cherrypy.server object expanded (too far) in 3.0, trying to be a single interface for multiple HTTP servers. Now that we have a unified startup/shutdown process in the Bus, that isn't needed anymore and should be removed; cherrypy.server should go back to being an adapter for a single HTTP server. Users who wish to deploy multiple servers should wrap each one of them in a restsrv.servers.!ServerAdapter and subscribe them to the Bus.