Use a typeahead for "document types" in global search

Summary:
  - Now that we have "browse", this is a much more reasonable control for random sets of things.
  - The new explicit search scope selector reduces the need to fiddle with this field manually, too.

Test Plan:
{F379292}

{F379293}

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D12510

src/applications/phriction/herald/PhrictionDocumentHeraldAdapter.php

@@ -13,7 +13,7 @@ final class PhrictionDocumentHeraldAdapter extends HeraldAdapter {
     return pht('React to wiki documents being created or updated.');
   }
 
-  public function newObject() {
+  protected function newObject() {
     return new PhrictionDocument();
   }