Restyle the secondary nav.

I've checked this in community, the styleguide, and waldorf which covers both the `core` and `responsive` layouts. I've also made sure the `/legacy` route still looks ok.

If anyone can think of anywhere else I've missed that could/should be checked, please let me know!

![1402646582](https://cloud.githubusercontent.com/assets/708296/3267717/37ac7692-f2d1-11e3-87b7-e89a1b503e3e.png)

![1402662485](https://cloud.githubusercontent.com/assets/708296/3269878/79df4e16-f2f6-11e3-8a99-e8a6642df178.png)

I asked @Ianfeather and he said:

> It’s only for the /legacy placeholder page
> the apps provide their own secondary nav

Beyond that... ¯\\\_(ツ)\_/¯