Hide overflow text of constraints on small screens.

Closes #850 

#### Before
![breadcrumb-before](https://cloud.githubusercontent.com/assets/96776/4329396/4242b9ae-3f98-11e4-9236-c6a1944117b6.png)

#### After
![breadcrumb-after](https://cloud.githubusercontent.com/assets/96776/4329397/425af6cc-3f98-11e4-96d2-33e6fc4015a3.png)