This grabs the docs via the @pybricks/ide-docs package and copies them
to the build directory with copy-webpack-plugin.
The service worker automatically picks up these files for precache
since they go through webpack.
This package is a bit more versatile. For example, it lets us include
the app's package too.
webpack-license-plugin had a bug that made it unusable anyway.
This lets us modify some config without ejecting create-react-app.
This allows us to target esnext which works around a number of issues
with multi-targeted packages like blueprintsjs and react-i18n.
David Lechner