Allow multiple entry points with same basename

[fsateler]

This allows having eg, application.css and application.js

[gauravtiwari]

@fsateler Thanks 👍 and sorry this one has been hanging in for a while. Basically, the idea is to keep only Webpack entry files (JS) inside packs directory. Obviously, the main module can live anywhere inside the app/javascript or where ever the JS source is as long as it can be referenced and bootstrapped inside packs. The module should be responsible for all styles and assets instead of packs/entries. That way it will create the .css bundle for you after compilation (if any styles), which will be same name as entry/pack name. Does that make sense?