Enhanced Search results page view

Both HH and CPN have asked that:

* the search results page results list can be filtered by category
* category sets be refined into one master category list for use across the entire site

CPN also wanted site-wide cat­egories: We sort all con­tent added to the system into a global set of categories so res­id­ents can quickly dis­cover anything on the site relating to their own area of interest.

I'm wondering if we use something like Solr, could we build this or is it something we can build ourselves perhaps as a View (a la this https://www.lullabot.com/articles/custom-search-forms-with-views-and-fastsearch)

No files, tests, or entry points are named. Start by locating the Drupal search results implementation and the existing category definitions, then determine whether Solr or Views is appropriate; done would mean filtered results and one shared category set across the site.

Written by the indexing model from the issue text.