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