Refactor FacetapiAdapter::__construct() for better testing

Various components should be refactored for better unit testing. Since the logic is jumbled in the __construct() method, it makes it difficult to test as there are no return values to work with. The areas that could be moved into separate methods are the following:

• Getting and setting valid query type for the adapter's enabled facets.
• Loading and setting the URL Processor plugin.
• Initializing the URL Processor plugin by fetching, normalizing, and setting the params.