Created by: ryansully
Adds navigateFallbackWhitelist to service worker precache config options in Webpack config for production builds. This solves an issue with Firebase reserved URLs not working due to the PWA service worker serving the navigateFallback URL (/index.html) when non-cached URLs are requested.
Fixes part of https://github.com/facebookincubator/create-react-app/issues/2237, specifically https://github.com/facebookincubator/create-react-app/issues/2237#issuecomment-302693219.