Interwork smoothly with GAP saved workspaces

[stevelinton]

There are a couple of things it would be nice to do, possibly of various levels of difficulty:

• Start a notebook with a GAP kernel from a saved workspace specified somewhere, inlcuding one
  which was created from a non-jupyter GAP session

• Somehow pair up a .ipynb file and a GAP workspace, so that you can save state and get back to where you were without having to rerun possibly very expensive computations