Search: improve performance of the javascript bundle

The js bundle for instant search is 33kb (and probably growing). We've done a lot to keep it small, but it rivals jQuery now. Can we lazy load it, and also make sure that it always loads from our CDN to make it more likely that it will be cached?

Some corner cases where this may break:
- User goes to a url for search results, then we should not lazy load it since the correct results won't be displayed until the js has loaded. There may be other cases like this in the future too.
- Do we need to break out any js so that it can be applied to the elements on the page? Thinking about the search box in the widget and any filter links on the page.

We should probably be optimizing for https://developers.google.com/speed/pagespeed/insights/

Start by locating the instant search JavaScript bundle and the code that loads it. Trace search-result URLs, the search widget, and filter links to identify what can be lazy-loaded or served from the CDN; done means those cases still work and the bundle's loading improves the PageSpeed result.

Written by the indexing model from the issue text.