[cobweb model] Animated Plots

[mmcky]

It might be nice to develop animated plots of the dynamics for the 45 degree line when technology allows.

[mmcky]

This could be a good candidate for wasm compatibility and then interactivity would be from running code (in browser) rather than saving large animated figure objects.

[longye-tian]

This issue is closed and followed by #533.

Best,
Longye