panel and button classes

[harrybigspring]

I think we should remove the "default" option for these and simply have:

primary
secondary
tertiary (usually the bordered style)

[juliotaylor]

These should mirror the classes in Foundation 6 (once we've made the switch):
http://foundation.zurb.com/sites/docs/button.html#coloring

Outline buttons are also handled as "hollow":
http://foundation.zurb.com/sites/docs/button.html#hollow-style