webpack

Add `react-router` and `@loadable/components` to demo lazy loaded code splitting.

Add file-loader and url-loader, some example images and a font.

Convert to use babel-loader. Add hot module replacement. Add counter subcomponent and state to AnotherApp for demo.

Add mini-css-extract-plugin to extract CSS imports for production builds. Add postcss and autoprefixer to handle vendor prefixes.

Add CSS related loaders, leave CSS inline in production build.