Implement: ES6 modules

[andygout]

Development app will run (using $ npm start) server/app-dev.js, transpiling at runtime using babel-register.

Tests ($ npm test) will transpile server code into a dist directory (via 'pretest' command) and test that code.

TO DO: At production stage the app will run the dist directory code (to improve performance as will not have to continually transpile). This will require step to create dist directory and for Procfile to point at that.

New dependencies:

• npm: babel-cli
• npm: babel-plugin-add-module-exports
• npm: babel-plugin-transform-es2015-modules-commonjs
• npm: babel-register

References:

• Stack Overflow: Cyclic dependency returns empty object in React Native - solution to cyclic dependency that exists between Production and Theatre models.
• Financial-Times/next-api - other implementation of running production and tests from transpiled code and dev transpiling at runtime.
• GitHub: andygout/theatrebase - previous implementation of ES6 modules in this app.
• GitHub: motdotla/dotenv (Issues) - Using with ES6 modules - Solution to using dotenv with ES6 modules as provided by ngzhian on Oct 21, 2016.

Run tests transpiling at runtime (not from dist directory):

• Amend package.json (removing pretest command) so as to require spec/server/setup file:
  "test": "find spec -name '*.spec.js' | xargs mocha --require spec/server/setup -R spec"

• Add spec/server/setup.js:
  require('../../server/setup');

• Add server/setup.js:

require('babel-register')({
	plugins: [
		require.resolve('babel-plugin-add-module-exports'),
		require.resolve('babel-plugin-transform-es2015-modules-commonjs')
	]
});

• Convert all spec files to use ES6 modules syntax.