Fixes #13047, #16291 - Upgrade datatables and move it to npm

fixes #15806 - Add linting to webpack

This commit adds linting to webpack processing via eslint.

Fixes #16120 - Allow including css in webpack assets

This commit demonstrates using the css from the select2 module using the
webpack css loaders. Images under 32k will be compiled into the css to
reduce request counts.

fixes #16089 - replace flot-rails with npm jquery-flot

Fixes #12364 - Use NPM+Webpack to handle external assets

This commit introduces NPM and Webpack to handle external assets.
It also provides ES6 support and a live reload dev server that can be
used by running `foreman start` instead of `rails start`.
Do not forget to run `npm install` before starting the server....