Webpack 5 + Build updates

[goto-bus-stop]

This PR:

• Updates webpack and all webpack related dependencies
• Updates material-ui to v5
• Removes rollup: just using webpack for the middleware, it sucks, but it's easier
• Removes the ability to run the server + web client in one process for development
  • It was outdated and didn't work
  • It's kinda easier to run them both manually rather than setting up all the symlinks
• Removes gulp: no longer needed for orchestrating server+client setup, nor for middleware building

Todo:

• middleware package.json should use a different webpack hook
• wait for plugins to fix uses of deprecated features
  • webpack-subresource-integrity
• can we get rid of extract-loader in this PR?