Config Not Editable for Variants without a Config Form

[JonKo314]

The Fractional Go demo just uses the default config for Fractional Go and doesn't allow changing it. This is probably because Fractional Go doesn't have a config form yet.

• Option 1: Add config forms for all variants
• Option 2: Allow editing of raw JSON config for demos

[benjaminpjones]

I'd recommend a hybrid approach: introduce a JSONConfigForm, and use it by default.

I think we should also strive for real config forms for all variants (1), but that can be a pain for prototyping.