Graphical debugging of mutations

[lhstrh]

The runtime already creates a DOT representation of the dependency graph at the start of the program. First of all, we should introduce a CLI option to disable this feature, since it is really just meant as a debugging feature.

That said, with mutations, the graph will change at runtime, so it would be great to track these changes graphically for debugging purposes. We could do this by running a web server that serves a page that displays the diagrams as they change. Lucky for us, there already exists an npm module capable of doing this: https://www.npmjs.com/package/d3-graphviz

[axmmisaka]

For reference, see https://gist.github.com/axmmisaka/f392d9ac97d6e97c6d501406f50ab635 and https://github.com/axmmisaka/reactor-ts/tree/sieve-visualize