Adds horizontal-nav to section (replacement for Nav Bar in v3) 

After upgrading a site I noticed there was no suitable replacement for the Nav Bar used in Foundation 3. The top bar is overkill for simple or secondary menus.

I've kept the code clean and succinct. The docs will need to be updated to include the extra use case:

``<div class="section-container horizontal-nav" data-section>``

Enjoy