Include Normalize.css if Bootstrap is not present

I included it instead of Bootstrap because Bootstrap already ships with Normalize. What do we do in the case when Sass & Compass are also present? Because then both Bootstrap and Normalize aren't included, which leaves `vendor.css` empty again. :worried:

Also, do I add Normalize to the description `Out of the box I include...` or is it unnecessary because Normalize is part of H5BP anyway?

This should fix #242 once it's resolved.