Circle thumbnails

Added circle thumbnails with and without padding and border.

![2013-12-09 09 46 07](https://f.cloud.github.com/assets/684942/1703609/a2913f84-60b8-11e3-84bd-29c57f51400e.png)
![2013-12-09 09 46 23](https://f.cloud.github.com/assets/684942/1703610/a29404e4-60b8-11e3-8de0-9a8f59f044ab.png)