Add auto update javascript

Make search results auto update when facets are changed on the finder.

This pull request does the following:

- Lifts the js from /alphagov/frontend/live_search and rewrites it using prototypes to match the style of the other js in this project.
- Modifies the js to work with this DOM and mustache config + updates tests.
This line doesn't do anything. You would need to call: `$.proxy(this.showLoadingIndicator, this)()` to execute it. It could just be `this.showLoadingIndicator();` though as it isn't inside a method where the this has been set to anything else.