Drop `fb-flo` in favour of webpack's hot replacement and `react-hot-loader`.

Lots of advantages: hot update works in any (?) socket enabled browser, magically updates React component preserving state (watch video at https://github.com/gaearon/react-hot-loader) in multiple opened browsers. No drawbacks found compared to `fb-flo`.

Also pack CSS into bundle. Consider extracting critical path CSS into HTML with
something like https://github.com/pocketjoso/penthouse to:

- prevent layout from flickering compared to js bundle packing
- make 1 request less compared to separate CSS file