Step events aren't appearing on canvas

[taylordowns2000]

Right now it looks like only step events are handled by the canvas, so we see workflows visualized only at the beginning (before any steps are complete) and at the end (when all steps are complete).

We'll need to "stream" steps and logs (eventually). This issue is to stream steps. In the video below, where each step has the code:

fn(state => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('wait, and then resolve');
      resolve(state);
    }, 2000);
  });
});

We should see each node light up in green after 2s.

https://www.loom.com/share/4d3d2112d2ad41ffbb5b7c3f9a90031c