create-react-app 4.0 released

- Fast Refresh
- React 17 support
- New JSX transform
- TypeScript 4 support
- ESLint 7
- New Jest and React Testing Library rules
- Jest 26
- PWA/workbox improvements
- Switch to the Workbox InjectManifest plugin
- Now its own template so it can be released independently
- Web Vitals support