react-spring: Animation playground

This uses NextJS as a base for quickstart. The styles are provided by Skeleton CSS.

Setup:

1. npm install
2. For dev: npm run dev
3. Other build tasks can be found in package.json scripts
4. localhost:3000 will show output. Hotloading and server side rendering are enabled by default thanks to NextJS.

Demo: https://afisher88.github.io/react-spring-playground/