Update the query when checking checkbox on demo

[raphael0202]

On the demo (http://search.localhost:8000/static/off.html), after the user entered a query, he/she can further filter the results by selecting one of the checkbox on the left side (ex: brands, categories,...).

When selecting a box, the updated search query (with the additional filter) is sent to the backend server, but the query that the user sees is not modified.
It's confusing for the user, as we're not sure whether the new filter works.
We should update the search input field as well.