* guix-jupyter-container.scm (proxy-exec-kernel): Get streams message
  type.
  (local-eval): Send 'guix-end-of-eval' message.
* guix-jupyter-kernel.scm (proxy-exec-container): Get streams message
  type.
* guix-kernel/jupyter-client.scm (reply-html): Send 'guix-end-of-eval'
  message.
* guix-kernel/jupyter-server.scm (exec-kernel): Add IPython.