Google Analytics support for _setDomainName

Many people setup their DNS settings in a way to treat domainname.com and www.domainname.com as equivalent. Google Analytics, by default, treats domainname.com and www.domainname.com as separate. To have GA track both top-level domain and sub-domains under the same report, _setDomainName() has to be used. 

More info here:
https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingSite#yourDomainName

This patch introduces a domain_name configuration for the Google Analytics widget. If set, _setDomainName() is called with the corresponding value.