Quantcast tracking

Adds support for a new tracking script from Quantcast, which will track users who successfully pledge via our website+scprcontribute and then allow us to target membership appeals to them when they visit other sites online.

Quantcast tracking needs to be added to the following pages:

* Homepage
* /about/
* /support/
* /listen_live/

Since /support/ is a flatpage, the tagging has been added directly to the flatpage in the CMS. The remaining pages need tracking code added to their views; the code is *mostly* identical, but a specific page title must be merged into the tracking script in two places. This page title can contain spaces when merged into  app/views/shared/scripts/_quantcast.html.erb on line 15, but on line 19 any spaces in the page title must be converted into pluses.