replaced the png icons with an svg icon with a stylized grunt

![image](https://cloud.githubusercontent.com/assets/5382443/4488632/7d9c76fc-4a10-11e4-88d7-6407224088a7.png)

![image](https://cloud.githubusercontent.com/assets/5382443/4488634/83dc19b4-4a10-11e4-9eba-5b4b09bbc19d.png)