Google analytics integration

- Use the same account for all instances of the site (for the moment)
- Google Analytics tries to avoid tracking people if they aren't on a subdomain of a domain you set (our domain is "service.gov.uk")
    - If you use ```--debug``` this behavior will be disabled (ie: you'll send requests when on localhost:7777)
- Use the [Google Analytics Debugger](https://chrome.google.com/webstore/detail/google-analytics-debugger/jnkmfdileelhofjcijamephohjechhna) to debug issues