New product comparison table added

This has been added, currently on /basic and /pro pages, as shown below.

Do we really want the links to also point to /basic and /pro, or somewhere else?

I'm hoping to still make the SVG's accessible (once I've resurrected & merged the alt-text branch).

![screen shot 2014-11-11 at 17 36 41](https://cloud.githubusercontent.com/assets/2903904/4997731/590c5cfc-69c9-11e4-9749-5b17d01d0d23.png)

Would be best if this states as explicity as possible what it's for, so class should really be `u-background-dark-gray-darken`