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
