feat(rxApp): allow expand/collapse of child menus

Finally got this one in. 

![image](https://cloud.githubusercontent.com/assets/706039/2724948/bda65756-c5a7-11e3-8be2-7d312f23dcb1.png)

Once all this rxApp/rxNav stuff is actually implemented I'll get into adding some major documentation on how to use it all.