Add better spacing between groups in curated topics.

Before:
![screenshot 2014-09-04 12 14 44](https://cloud.githubusercontent.com/assets/109225/4148411/b2ba38b2-3424-11e4-8943-929ecb470578.png)

After:
![screenshot 2014-09-04 12 15 06](https://cloud.githubusercontent.com/assets/109225/4148415/bf332144-3424-11e4-98d7-9e1099dd4820.png)