Improve ordering of main typeahead results

Summary:
Always order applications first, then users, then other results (currently, there are no other results, of course).

(This is similar to the general ordering algorithm used in JX.Prefab but has enough current/future differences that I split it rather than trying to share them.)

Test Plan: Queried results, verified order.

Reviewers: vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3117