Add Google site verification meta tag support

[markmhendrickson]

This entails adding support for inserting a meta tag into the head using the value of the googleSiteVerificationContent attribute when available.

This would allow the website to continually make itself available to Google webmaster tools for verification whenever Google wants to (re)crawl the site for that purpose.

Example

<meta name="google-site-verification" content="XXXXXXXXXXXXX" />