- This also works just as well as a REST endpoint.

- Most likely this is just a demo. But it works for that.

I'll only need it for a demo, probably. But it's nice to have.

Should be enough to (1) talk to the Java API and (2) provide
a JSON API for the world.

This is really just experimental. MMT should be integrated directly
w/o JSON if possible to avoid nonsensical serialization.