Add Google Analytics Universal

This pull request does three things:

 - Google Analytics has a new version of its tracking code out refered to (sometimes) as 'Google Analytics Universal'. This is added beside the existing Google Analytics ('Classic', if you will) code. So, if for some reason you wanted to, you could run both at the same time.
 - Document the above. The new variables are `GOOGLE_ANALYTICS_UNIVERSAL` and `GOOGLE_ANALYTICS_UNIVERSAL_PROPERTY`
 - do a little bit to standardize the indentation of the various tracking code snippets