Commercial modules refactor

Made them more self-contained (but switch checking logic in them), and also added tests

Also testing out [Squire.js](https://github.com/iammerrick/Squire.js/) as a way of mocking RequireJS' dependecies - https://github.com/guardian/frontend/blob/commercial-modules-refactor/common/test/assets/javascripts/spec/commercial/article-body-adverts.spec.js,

cc: @jamesgorrie