Vertical nav component

Still extends the left nav for now. Should take all the possible variations of links we have.

We can definitely normalise our nav components; the current left nav, nav submenu components and this component share many traits.

Example usage: https://github.com/lonelyplanet/waldorf/blob/679fa13c2b5889fda15f0b8369e26bd6529dbcb0/app/views/place/_layout_responsive.html.haml#L22-L30

Related:
https://trello.com/c/dtKFeJg4/223-normalise-and-dry-nav-submenu-left-nav-and-vertical-nav

![screen shot 2014-12-08 at 18 06 28](https://cloud.githubusercontent.com/assets/271645/5344213/073c999a-7f05-11e4-8fbc-12a0c156b99b.png)

Also moves some of the general ad rail layout into rizzo and fixes display of ad rail ads on smaller screens:

![screen shot 2014-12-09 at 11 20 34](https://cloud.githubusercontent.com/assets/271645/5356523/6fd1c5f8-7f95-11e4-81e0-d78d057e004e.png)


What's the reason we can't just have single direction margins here?