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/maniphest/controller/ManiphestReportController.php

@@ -380,7 +380,7 @@ final class ManiphestReportController extends ManiphestController {
 
     $query = id(new ManiphestTaskQuery())
       ->setViewer($user)
-      ->withStatus(ManiphestTaskQuery::STATUS_OPEN);
+      ->withStatuses(ManiphestTaskStatus::getOpenStatusConstants());
 
     $project_phid = $request->getStr('project');
     $project_handle = null;