fix hitting back on nav, use more css over js for active styling (bug 1058996)

The behavior of the nav should remain the same. Except this fixes hitting "back" on desktop (i.e., there was duplicate pushStates, and hitting back didn't update the nav activness). Fixed by:

- remove duplicate navigation triggering
- defining the tab activeness in CSS using body[data-page-type] rather than CSS
see my comment above. we made this same mistake in Martellplace and it was a mess. I spent a lot of time in AMO and the multiple redesigns of the Marketplace trying to undoe these same type of mistakes. one-offs and high specificity and verbose selectors make it a pain to maintain CSS in the long term. and you get tons and tons of visual papercut bugs.