Use ManiphestTaskQuery in nearly all interfaces

Summary:
Ref T603. Make almost every task read policy-aware. Notable exceptions are:

  - Edge editor -- this stuff is prescreened and should be moved to ApplicationTransactions eventually anyway.
  - Search/attach stuff -- this stuff needs some general work. The actual list should be fine since you can't pull handles. There may be a very indirect hole here where you could attach an object you can't see (but do know the ID of) to an object you can see. Pretty fluff.
  - The "Tasks" field in Differential will let you reference objects you can't see. Possibly this is desirable, in the case of commandeering revisions. Mostly, it was inconvenient to get a viewer (I think).

Test Plan:
  - Called `maniphest.info`.
  - Called `maniphest.update`.
  - Batch edited tasks.
  - Dragged and dropped tasks to change subpriority.
  - Subscribed and unsubscribed from a task.
  - Edited a task.
  - Created a task.
  - Created a task with a parent.
  - Created a task with a template.
  - Previewed a task update.
  - Commented on a task.
  - Added a dependency.
  - Searched for "T33" in object search dialog.
  - Created a branch "T33", ran `arc diff`, verified link.
  - Pushed a commit with "Fixes T33", verified close.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7119