Make column reordering after edits on workboards more general

Summary:
Ref T5476. Currently, the task edit code assumes it knows what the UI looks like and sends back where on the column an item should be inserted.

This is buggy after adding filters, and relatively complex. Instead, send down the ordering on the whole column and sort it in the UI. This is a bit simpler overall and more general. It makes it easier to further generalize this code for T5476.

Test Plan:

• Edited a task on a board, changing priority. Saw it reorder properly.
• Edited a task on a board in a field of other tasks at the same top-level priority. Saw it refresh without reordering.

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5476

Differential Revision: https://secure.phabricator.com/D9832