fix(menu): Update active menu determination logic

This fixes too rxMenuItem matching too much if multiple items have a url containing, for example, `/accounts`.

![image](https://cloud.githubusercontent.com/assets/5025474/3881857/6699530a-2191-11e4-9e2c-fb15c94e6f85.png)

What's going on with this line? It looks like:

* Taking a substring of everything except the first character (`substring(1)`)
 * Re-grabbing all of that string? (`substring(0, itemUrl.length)`)