Restructure examples so each example has a simulation.json in it

[andeplane]

In order to support #50, I want each Simulation to consist of a JSON file with all data. The structure should be the contents of each example in the examples.json file, including inputScript and previewImage.

Then we can better setup for your simulations, where we reuse the file system of JupyterLite so we have one file system in sync.