Use typeaheads instead of checkbox lists for task status / priority

Summary:
Ref T4100.

This makes it slightly harder to choose, say, all priorities above X or all priorities except Y. We could add open(), closed(), min(), max(), and not() functions if there's a meaningful demand for them. I suspect some of these are maybe worthwhile while others aren't as worthwhile.

Test Plan:

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4100

Differential Revision: https://secure.phabricator.com/D12528