This is so that these can be reused (e.g.: for
specifying a nixos jupyter service kernel).

Moves package from using jupyter-notebook to the jupyter-lab.
Both backends can still be used using: ihaskell-notebook and
ihaskell-lab respectively.

This improves Nix compatibility without changing Stack or Cabal
compatibility. See #728.

This module takes an incredibly long time to compile and I haven't
missed it. If needed, it can be enabled with e.g.
`--arg packages '(p: [ p.ihaskell-widgets ])'`.