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 error message has a typo (trying). It's also probably not very useful. If the user encounters an error, is tweaking the search params really the most likely way of them being able to fix it?