Use render-code instead of old renderer

Expected behavior:

Can type demo.gif into editor, rendering with render-code.

Current behavior:

We are using render-code to render a demo, but editing doesn't work at all.

Tasks:

[x] Use render-code for initial rendering, with new demo
[ ] BLOCKED Update demo to match whatever render-code demo ends up looking like, with tree-based loading
[ ] Get edit loop to run without errors
[ ] Make sure editor events are getting sent properly by the edit loop
[ ] Get DOM updates to work with render-code

erikpukinskis / write-code