When creating or editing a card on a sorted/grouped workboard, adjust headers appropriately

Summary:
Depends on D20270. Ref T10333. If you create a task with a new owner, or edit a task and change the priority/owner, we want to move it (and possibly create a new header) when the response comes back.

Make sure the response includes the appropriate details about the object's header and position.

Test Plan:

• Grouped by Owner.
• Created a new task with a new owner, saw the header appear.
• Edited a task and changed it to give it a new owner, saw the header appear.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T10333

Differential Revision: https://secure.phabricator.com/D20271