Optimize bundle output

[Thesephi]

As of writing time, doing npm run build (to generate a production build) shall emit these warnings:

WARNING in asset size limit: The following asset(s) exceed the recommended size limit (244 KiB).
This can impact web performance.
Assets: 
  js/main.js (662 KiB)

WARNING in entrypoint size limit: The following entrypoint(s) combined asset size exceeds the recommended limit (244 KiB). This can impact web performance.
Entrypoints:
  main (662 KiB)
      js/main.js


WARNING in webpack performance recommendations: 
You can limit the size of your bundles by using import() or require.ensure to lazy load some parts of your application.
For more info visit https://webpack.js.org/guides/code-splitting/

Would be nice to take those advices into account & optimize as much as we can out of this process.