convert a keyword search into a faceted term search

* provided we can convert the search keyword into an authoritative facet term
* if more than one facet is matched, we'll use the first one with the highest priority configured

related to this [pull request](https://github.com/GigaOM/gigaom/pull/5114)

see https://github.com/GigaOM/legacy-pro/issues/3995
does the order of terms matter? in your example, we'll actually end up with an url that looks like http://search.gigaom.com/company/ibm+apple/, because we added a new company facet "apple" to the existing company facet "ibm". Alternatively we could alphabetize the list of facet terms but I don't believe we're doing that now.