feat(rxApp): updated design of collapse button

Just some minor style updates to the collapse button to address #200 

View movie of it in action here:
https://s3.amazonaws.com/uploads.hipchat.com/50699/423052/I4okW2pYlsfrxHZ/rx-app-collapse-update.mov

![image](https://cloud.githubusercontent.com/assets/706039/2975981/170c5864-db9b-11e3-9e0f-f4636350abb4.png)
![image](https://cloud.githubusercontent.com/assets/706039/2975985/2126e418-db9b-11e3-891a-f300c588aacd.png)