Search text label

The search text label should be displayed on tablets on desktop clients, but not on mobile.
In order to test whether or not this has the intended outcome, I've added an A/B test for it.

![screen shot 2014-05-12 at 16 48 15](https://cloud.githubusercontent.com/assets/1492162/2946925/9600f820-d9f0-11e3-99c8-6149dc940dcf.png)
![screen shot 2014-05-12 at 16 48 32](https://cloud.githubusercontent.com/assets/1492162/2946926/96199470-d9f0-11e3-8084-cee3fef91e0d.png)