Simplify build / test workflows

[renchap]

The goal is to create rake tasks to :

• Install/update JS dev dependancies
• Run linters (rubocop and eslint)
• Build the JS code
• Link the NPM package to register it for local use
• Run webpack for the test application
• Run tests

The README will need to be updated as well.

I will probably move javascript/webpacker_react-npm-module/ to the root directory, as it makes more sense for it to be here.

[sevos]

moving would allow referencing the github url of the package in packages.json if someone would like to use edge version :)