Mostly replace the old panel "Edit" controller with the new "Editpro" controller

Summary:
Depends on D20370. Ref T13272. This tries to get panel editing fully on the newer "Modular Transactions" + "EditEngine" flow.

This breaks tab panels a bit, but I'll fix that in a followup. And they weren't exactly in great shape before.

Also makes the flow prettier. :3

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13272

Differential Revision: https://secure.phabricator.com/D20371