Jupytext native py files as notebooks

[jlubken]

Jupytext allows annotated pyy:light to render and operate as notebooks. However, editing the .py file directly and reloading from disk does not merge/sync changes to the "notebook view", but instead destroys the output cells and syntax highlighting.

We could setup the py file metadata to sync to ipynb files to enable reload, but this would mean that users must:

1. Open the .py file as Notebook
2. Save to produce the ipynb
3. Shutdown kernel
4. Open ipynb with new kernel

This just doesn't work as a workflow. Checking in the ipynbs defeats the purpose of jupytext: lint on .py file and merge into notebooks while keeping output cells and PHI out of source control.

---

I suspect that the settings for jupytext may be incorrect. Alos look at upcoming features of unreleased jupytext to see if this is being worked on.

---

Also two pass jupytext pre-commit insanity