Add Pinterest Pin-It functionality to lightboxes

The following changes add Pinterest Pin-It functionality, providing a sub-set of the "Pin-It Button" functionality found here: http://business.pinterest.com/widget-builder/#do_pin_it_button

- Changes  in the 'settings' allow this feature to be turn on and off
- If the feature is turned on, the lightboxes will have a pin-it button as illustrated in the image below:

![screen shot 2014-04-27 at 11 09 50 pm](https://cloud.githubusercontent.com/assets/164866/2813278/b3b5eba6-ce82-11e3-918f-4f39844968bd.png)

Pinterest images link to the site URL.

This is my first pull-request for a github project, so if I've done something wrong, please feel free to let me know.