Set $can_edit for Harbormaster steps

Summary: Sets the `$can_edit` value correctly (previously it was hardcoded to `true`).

Test Plan: Went to http://phabricator.local/harbormaster/step/view/1/ and saw "Edit Step" disabled.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14373

src/applications/harbormaster/controller/HarbormasterStepViewController.php

@@ -97,7 +97,10 @@ final class HarbormasterStepViewController extends HarbormasterController {
       ->setUser($viewer)
       ->setObject($step);
 
-    $can_edit = true;
+    $can_edit = PhabricatorPolicyFilter::hasCapability(
+      $viewer,
+      $step,
+      PhabricatorPolicyCapability::CAN_EDIT);
 
     $list->addAction(
       id(new PhabricatorActionView())