Don't show closed typeahead results while open results exist

Summary:
Ref T4420. When a result list contains both open and closed results, hide the closed results. I think this has a good chance of almost always working, and feeling very intuitive. It has a small chance of being a weird mess. It feels reasonable to me so far

The one bad case I can come up with here is that if you have results which shadow each other, like "Apples" (a closed project) and "Apples and Bananas" (an open project), it is impossible to get "Apples" in the result list, because "Apples and Bananas" will always shadow it. Let's wait for someone to hit this before we figure out how to deal with it.

Test Plan: Typed through open stuff to hit closed stuff.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D8238