Consider ejecting from react-scripts

[GeorgSchneider]

We are currently forced to use react-rewired-app to be able to provide a custom webpack config for polyfill overrides. If we want this demo app to be a starting point / app skeleton that customer can actually use, we should consider ejecting from react-scripts to have more explicit config options and less magic.

There are a couple of "hacks" that the app uses to run smoothly locally, that we'd need to mark clearly as not supported in production if we do this (eg. the parties.json file, or the generation of dummy tokens).