Bundle Python and install datasette in a virtual environment on startup

[simonw]

Refs #25.

[simonw]

I'm going to see what happens if I have the test.yml workflow run npm run dist at the end and then attach the generated .dmg file as an artifact.

[simonw]

That took longer than 5 minutes (total including running the tests) so it timed out.

[simonw]

Got this error:

⨯ GitHub Personal Access Token is not set, neither programmatically, nor using env "GH_TOKEN"

[simonw]

electron-userland/electron-builder#1693 (comment) says I should pass --publish=never

[simonw]

OK that seemed to work... there's a 150MB DMG artifact attached to https://github.com/simonw/datasette-app/actions/runs/1188102495

[simonw]

It totally worked!

I downloaded the artifact and installed the application from the DMG (to /Applications/Datasette.app) - then I ran it and it told me I couldn't because it wasn't signed.

So I went to Security & Privacy in the system preferences and clicked "open it anyway"... and it launched and installed everything it needed into ~/.datasette-app/venv and the application worked!