Standardize JSON exporting

(1) When rendering an image, the parameters are written back to a file in the output directory alongside the rendered image and diagnostics. But, they are generated from the fractal-specific parameters (eg. BarnsleyFernParams), rather than the top-level FractalParams. This means, that if you try to directly pass them to the render command, without wrapping them in the type annotation, that the render command will fail.

(2) The explore mode only exports the ImageSpecification data to the JSON, but it should explore the entire FractalParams, with the updated image specification details.

Perhaps both of these can be fixed with a similar technique.