Hi,

this patch series adds Jupyter’s JupyterLab, which is the new frontend for
Jupyter Notebooks. The software works fine, but there are a few caveats

1) it comes with bundled pre-compiled JavaScript, which cannot be removed until
   we have proper support for importing from NPM
2) it contains an extension manager, that downloads arbitrary packages from NPM
   (`jupyter lab build`). This works, but is less than optimal imo. We should
   figure out how to package extensions in guix.
3) also it is required to install the package `jupyter`, otherwise installed
   kernels cannot be found and the `jupyter` command does not work.

Cheers,
Lars