Add 'Kill' button to query.html

This patch adds 'Kill' button to query.html page.

The button looks like this if the query is running:
![running](http://gyazo.com/ea79154feecb520895a940f476cab4a6.png)

When you click the button and reloads the page:
![killed](http://gyazo.com/e1f9721086d0aedba4baf0982a7f4b30.png)