Front end build setup

- There are some tasks we do to take the CSS, Javascript and images that we create and transform them into things that can be served to the user.
- We use a tool called [Grunt](http://gruntjs.com/) to automate these tasks
- The tasks are defined in `Gruntfile.js`
- `app/assets/` now contains the code that we work on
- `public/` now contains the generated code (no longer in version control, anything you put in here manually is liable to get overwritten)
- `node_modules/`, `govuk_modules/` and `bower_components/` are for temporarily storing things that come from the internet. Not version controlled and won't show up until you run the tools
- `bower.json` and `package.json` are for managing dependencies

TL;DR If the app looks wrong, run `npm install -g grunt-cli && npm install` before doing `play run`