Make projects policy-aware

Summary: We managed to move enough Owners stuff aside to make this reasonable; make projects implement the policy interface and projectquery use cursor-based paging.

Test Plan:
  - Grepped for ProjectQuery callsites.
  - Created an audit comment.
  - Used `project.query` to query projects.
  - Loaded homepage.
  - Viewed Maniphest task list, grouped by project.
  - Viewed project list.
  - Created / edited project.
  - Browsed Owners.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D3200

src/applications/directory/controller/PhabricatorDirectoryMainController.php

@@ -40,6 +40,7 @@ final class PhabricatorDirectoryMainController
       case 'home':
       case 'feed':
         $project_query = new PhabricatorProjectQuery();
+        $project_query->setViewer($user);
         $project_query->withMemberPHIDs(array($user->getPHID()));
         $projects = $project_query->execute();
         break;