Refactor navbar to eliminate nested {{link-to}}.

This is essentially setting up a binding from the `LinkView`'s `active`
status and whatever is set as `alternativeActive` in the `{{link-to}}`
(in our case the `activating-list-item` component.

Screenshots showing that the proper CSS classes are given:

![screenshot](http://monosnap.com/image/tzOH6n82rIVGNEFAUWVOLN52QuASQ4.png)

![screenshot](http://monosnap.com/image/5gmcwJcj0kgEXt8lnET4OKgIZ8KRpH.png)

![screenshot](http://monosnap.com/image/UCVNukTXLMNfVneLhzwVyhkrVlGSBt.png)