Add .buildpacks file per ddollar/heroku-buildpack-multi

See https://github.com/ddollar/heroku-buildpack-multi
Enhance asset:compile_environment task to use webpack to create rails-bundle.js
Heroku setup

per: https://devcenter.heroku.com/articles/getting-started-with-rails4
Move package.json to top level for heroku deploy
Add node_modules
Update package.json to include react-tools
No sourcemaps on production
Updated README