Testing e2e

[jvalkeal]

Experiment creating tooling to run shell app as a black box to do e2e testing where we should only care about what is typed into a shell and what shell is showing.

Realistically this is impossible to do in plain java, afaik, so should try to see how far we get using node and integrating with node-pty and xterm-headless. Many online shell tools use these libs to hook into an actual shell which can then run commands. We only need to be able to pass keystrokes and read what term things is shown in a "screen".

[jvalkeal]

Initial work done.