Empty states

Adds helpful text to empty parts of the UI:
![screen shot 2014-04-16 at 12 57 35 pm](https://cloud.githubusercontent.com/assets/108094/2722461/4c75ea3e-c588-11e3-9f13-df25562a3cff.png)
![screen shot 2014-04-16 at 12 58 44 pm](https://cloud.githubusercontent.com/assets/108094/2722470/639f7b12-c588-11e3-875a-ce73b70688c4.png)