Add graphs for causal inference

[marimeireles]

It seems like it should be pretty straightforward!
whynot gives us the graph topology already (wn.causal_graphs.build_dynamics_graph) so we just need to model it and use a graphic library to show it.
I think I have an idea on how to use graphviz for this. But open to suggestions and other people taking this.
It's mostly a suggestion for what I perceived as a low hanging fruit.