Add clearView link while searching

See #1517

![image](https://cloud.githubusercontent.com/assets/339611/3944416/863fe86c-2601-11e4-8911-bbfc65ca04f1.png)

http://www.reddit.com/search?q=test&sort=relevance&t=all#res-clear-view
Although clever, using :target ~ .... { display: block|none } seems brittle because it relies on the buttons being in a particular place in the DOM; also, I suspect it will break if you follow a link to another #anchor.

I'd recommend just adding simple JavaScript click handlers on the buttons to toggle a CSS class.