Fixit: Adds G+ icon w/link to Puppet Labs G+ page

A goodly number of the Puppet Labs docs pages are incorrectly attributed to Jeff McCune in Google search results, most likely owing to Google incorrectly treating links to the Pro Puppet book as a byline for content on docs subdomain pages. 

This commit attempts to rectify that issue by:

- Adding a link to the Puppet Labs Google+ page
- Adding an icon of the same dimensions and general look as the other social networking links
- Adding a "rel publisher" attribute to the link to the Puppet Labs Google+ page