Add and use Hot Module Replacement plugin and react-hot-loader
Move react-hot-loader to devDependencies
Add simple tests for HMR usage
Backport https://github.com/gaearon/react-hot-boilerplate/commit/58dddfd80d7a39083195a8da68849b5c898d9e8c
Merge pull request #29 from ColCh/feature/live-edit

Use HMR api (livereload for app)