3D Visualizer

[nadarenator]

This PR adds:

• 3D visualization using Matplotlib.
• Colorbar legend for plotting rollouts.

TODO:

• Update docstrings.
• Fix 2d rendering.
• Fix Z-ordering.
• Update visualizer demo.
• Restructure nested function calls.
• Dark Mode.

[daphne-cornelisse]

A couple of comments on the visualizer:

• What is the extend_goals argument for? Can we convert this to a util function instead of having the code as part of plot_simulator_state()?
• Could you make sure that the arguments are briefly described in the docstrings?

[nadarenator]

* What is the `extend_goals` argument for? Can we convert this to a util function instead of having the code as part of `plot_simulator_state()`?

It plots where the goals would be if they were behind the agents. Useful to screen for plausible scenes in hand-designed experiments. Its better off as part of the plot_simulator_state() function in my opinion, because it uses a lot of the local variables (such as the sim object).

* Could you make sure that the arguments are briefly described in the docstrings?

Will do!

[daphne-cornelisse]

Looks great! Feel free to merge