Expose column positions via maniphest.edit

Summary: Ref T5214. Fixes T10486. Ref T6027. This exposes the TYPE_COLUMNS transaction in a usable way via API, and fixes the interactions via prefilling.

Test Plan:

• Created tasks directly into columns via API.
• Moved tasks between columns via API.
• Used ?column=... to try to create a template task with valid and bogus column PHIDs.

Reviewers: chad

Reviewed By: chad

Subscribers: AmyLewis

Maniphest Tasks: T5214, T6027, T10486

Differential Revision: https://secure.phabricator.com/D15636