- Make server extension authenticated
- Try to determine if running with adjacent notebook server,
  and if not, spawn static file server from which to provide
  web modules. This will probably just be used by VSCode.
- rename _jupyter_server_base_url to _import_source_base_url
  to better indicate that this is a manually specified
  location where web modules are served rather than a jupyter
  server (though it might be).
- bump model and view versions for everything.