Move many task status hardcodes into ManiphestTaskStatus

Summary:
Ref T1812. This cleans up most of the easy hard-coded references to specific statuses:

  - The "fixes" language moves into ManiphestTaskStatus.
  - Add a method to list open statuses.
  - Add a method to test if a status is open.
  - Add a method to get default status for new tasks.

Test Plan: Browsed around, lint, grep, created, filtered and updated tasks.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1812

Differential Revision: https://secure.phabricator.com/D8264

src/applications/project/controller/PhabricatorProjectBoardController.php

@@ -51,7 +51,7 @@ final class PhabricatorProjectBoardController
     $tasks = id(new ManiphestTaskQuery())
       ->setViewer($viewer)
       ->withAllProjects(array($project->getPHID()))
-      ->withStatus(ManiphestTaskQuery::STATUS_OPEN)
+      ->withStatuses(ManiphestTaskStatus::getOpenStatusConstants())
       ->setOrderBy(ManiphestTaskQuery::ORDER_PRIORITY)
       ->execute();
     $tasks = mpull($tasks, null, 'getPHID');