Some webpack stuff

[hypercross]

The webpack setup could use some work.

• worker-loader is deprecated under webpack 5, which throws an error during installation.
• index.js should probably be converted to a module type, to support the import.meta.url required for worker under webpack 5.
• @tensorflow/tfjs is the only huge bundled dependency of the project and should probably be externalized. Dev bundle size becomes ~200kb after this.
• could probably add a few lines of config to enable the dev server, in case anyone else is appalled by the ngrok nonsense like I am.