style subfigure and figure with/without caption

With captions:

![image](https://cloud.githubusercontent.com/assets/253202/3377596/f1a5efc0-fbe0-11e3-8d88-81e1b465a997.png)

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And without captions:

![image](https://cloud.githubusercontent.com/assets/253202/3377628/3a778c5e-fbe1-11e3-92d0-6c998cb32d94.png)