Bug 959582 - Refactor the search URL provider for the location bar. r=mak

--HG--
rename : toolkit/components/places/PriorityUrlProvider.jsm => toolkit/components/places/PlacesSearchAutocompleteProvider.jsm
rename : toolkit/components/places/tests/unit/test_priorityUrlProvider.js => toolkit/components/places/tests/unit/test_PlacesSearchAutocompleteProvider.js