workadventure: graphviz-based repository visualisation

This adds graphviz-generated visualisations of workadventure map repositories; all maps are nodes, all exitUrls are (directed) edges.

This just adds some static js & wasm blobs to render everything; the linter will provide fitting dot language expressions along with its output (as of commit 8f29266), limited to 7 steps from main.json to avoid crashing browsers with stuff like the CERT Hypercube.

The compiled javascript/wasm blobs are taken from unpkg/jsdelivr, except for d3-graphviz, which I built manually.

If the linter doesn't output a dot expression, this should quietly fall back to the same output as it was before.