Converting from Custom Webpack Config to Rails Shakapacker Config

1. Compare your package.json and the dependencies in https://github.com/shakacode/shakapacker/blob/master/package.json and avoid any duplicates. We don't want different versions of the same packages. We want the versions from shakacode/shakapacker unless we specifically want to override them.
2. Search the shakacode/shakapacker repo for anything you're not sure about in terms of package names.
3. Run bin/shakapacker and make sure there are zero errors
4. Update Webpack plugins and loaders to current or close to current
5. Make sure that your bin/shakapacker and bin/shakapacker match the latest on https://github.com/shakacode/shakapacker/tree/master/lib/install/bin