Layout members list on phone

Fix mix-it/linkit#322

On members list like http://localhost:9000/staff:
- make gravatar responsive
- reduced name font-size.

BEFORE:
![image](https://cloud.githubusercontent.com/assets/750715/5563920/0f88f35c-8e9e-11e4-940c-3915d24ec765.png)

AFTER:
![image](https://cloud.githubusercontent.com/assets/750715/5563921/147c6736-8e9e-11e4-994e-971493c80f2d.png)