Adding more list variables for flexibility

Hi there, love Foundation! First time pull request here. 

I love that you have `body-*` style for font option for general and now `paragraph-*` style for `<p>` tag, and was using them, but encountered an issue where list items inherited `paragraph-*` and not `body-*`.

This change will add flexibility by either keeping the current setup or overriding it.

Thanks for your consideration.