Use Maniphest own functions instead of hardcoded status

This patch changes to check for all open status, and for all closed status, not just "open" and "resolved".
It is kind of controversial in that it now returns all tasks that are closed, and not just the ones set to "resolved". This includes wontfix, invalid, or whatever other statuses have been set the closed: true property.
Differential Revision: https://phabricator.collabora.co.uk/D975