Add a jupyter server extension to render desktop/

A mess of a commit, should have been several.

- Finish renaming package from jupyter_desktop to
  jupyter_desktop_server
- Revert 360f9b04. Looks like
  websockify gets super confused when you put shell in the middle
  of it and the process it is spawning.
- Add a server extension that renders a slightly modified copy
  of vnc_lite.html as /desktop. This will be modified more and more
  as we go forward. This also helps us remove the mapping present
  in the jupyter server proxy entry