Change feed buttons (Unread/Starred/All) into tabs

This PR removes the bottom border of the selected feed view, i.e. it turns these buttons:
![screenshot 10-28-2014 at 3 41 18 p](https://cloud.githubusercontent.com/assets/510520/4811233/020f8232-5eb9-11e4-81f1-4989d7ab8e0c.png)
into these tabs:
![screenshot 10-28-2014 at 3 40 57 p](https://cloud.githubusercontent.com/assets/510520/4811232/0127f3e0-5eb9-11e4-8db3-1975918d736a.png)