Remove inline google analytics code

I've been investigating whether we can implement a stricter [Content-Security-Policy](http://en.wikipedia.org/wiki/Content_Security_Policy) for www.gov.uk. In order to make that effective we need to avoid inline scripts.

This is a quick pass at moving all the google analytics code out of the page. It seems to include the right things when I test it locally, but I'd welcome feedback from those who may know more about potential side-effects than I do (@edds @phae @bradleywright ?)