Streamcontroller react to locationchange

Our search is happening via setting the 'q' route parameter.
Our stream search has not reacted to it so only the default handler was fired, performing a page search.

Now we send a message to the backend via websocket and we get back the new search results from the backend. (As Expected)

Fix #1618
I use it here too: https://github.com/hypothesis/h/blob/e5ecce088ee8966651e114a90476da0769ce9ac5/h/static/scripts/streamsearch.coffee#L48