First-class webpacker support

[rmosolgo]

We should have a well-documented happy path for using webpacker + react-rails

Todo:

• support loading components from a pack refactor(UJS) make it webpack-friendly #678
• deliver UJS to packs refactor(UJS) make it webpack-friendly #678
• Generator should output to app/javascripts/components Support webpacker in generators #684
• documentation Redo Readme & update gemspec #685
• server rendering (static packs) Webpacker Server Rendering #683
• Support webpacker-but-not-sprockets environment Webpacker without sprockets #686
• Rename SprocketsRenderer? Webpacker without sprockets #686
• server rendering from dev-server Support server-rendering from webpack-dev-server #687
• Fix generated /components folder
• add UJS lookup fallback for hybrid webpacker-sprockets
• Update for webpacker path change Add a lookup_path helper that returns full pack path based on name rails/webpacker#237
• Deploy UJS to npm
• Update the description on GitHub

[gauravtiwari]

This is looking pretty good @rmosolgo 🎉 🍰

[rmosolgo]

:D Thanks! It's been a breeze working with webpacker, so thanks for your work on that!