Export model params as JSON

[chimaerase]

Following up to report/track some issues touched on in recent email discussions. My understanding is that N2A's current model.params files were usefully / thoughtfully hacked together as a stopgap. Exporting parameters as JSON might be useful to code / workflows derived from N2A, as well as making the files more self-describing.

For example, exporting parameters as JSON would eliminate the convert_model_params.py script in another app we're working on.

[frothga]

Agreed. JSON would be better than the current format.