Add support for +1/facebook like buttons, etc. (BB-4405)

I'd love to be able to include a 1 button for [[https://plus.google.com/106582181787882652415|my project page]] over on Google. A text field like the "Google Analytics" one that accepted the page ID, and added [[https://developers.google.com/+/plugins/+1button/#quick-look|a +1 Button]] somewhere in the 'repo-desc' would be great.

Alternatively, a way to include a +1 button in a Wiki page would work as well.