Kill the query through the web interface. Fixes #216

Show an icon to kill the query if it is running or accepted instead of the runtime (which is None anyway). 

![screen shot 2014-11-18 at 14 17 27](https://cloud.githubusercontent.com/assets/589034/5097267/bc847c2e-6f2d-11e4-940e-edad45ba1d65.png)