As per https://12factor.net/

Use environs/python-dotenv for reading/parsing variables

The npm configuration:
- Includes linting of javascript with eslint

The webpack setup here:
- Bundles javascript and css, using hashing to support server-side
  caching, with support from Flask-Webpack and
  manifest-revision-webpack-plugin
- Uses babel to transpile ES6 javascript
- Includes a development server with hot-replacing of javascript and
  css code

[fixes #11]

Bundle and minify css and js.