new navigation bar frontend (bug 957299)

http://screencast.com/t/rwmQVwKnd6

**Implementation Notes:**

- Have two navbars, one for Marketplace and one for Settings. They are both in the DOM, but one is hidden. ```navbar.js``` toggles between the two.
- Use ```hammer.js``` for swipe and tap gestures.
- Relies on ```body.data-page-type``` to know which navbar to show on page load.
- Popular, New, Category tabs stubbed out. Help tab stubbed out.

![screen shot 2014-02-28 at 2 32 39 pm](https://f.cloud.github.com/assets/674727/2299184/cb8a2a68-a0c8-11e3-9cf2-7f95346611ac.png)

http://people.mozilla.org/~mhanratty/feed_prototype_11082013/