re-add feed-app class to featured feed apps (bug 1101702)

before:

![](http://f.cl.ly/items/0A0G2y2y3z150m3m2A3M/Image%202014-11-21%20at%202.51.22%20PM.png)

after:

![](http://f.cl.ly/items/3y1g333S150c3S142Z2T/Image%202014-11-21%20at%202.51.49%20PM.png)