Namespace all CSS classes

[toolness]

This might be going overboard, but since webmaker-nav is meant to be embedded on arbitrary pages, I wonder if it'd be useful to namespace all its classes under e.g. wmnav-, so they don't conflict with pages' existing styles. Just an idea.

[k88hudson]

Yep, we should definitely do this.

Also, we could use a good reset, and probably avoid using h1, h2, h3, h4, h5 and maybe even p to prevent accidental inheritance.