Summary: Does the UI work that's part of T12234 and adds migrations for both of the old-style duplicate transactions.
Test Plan:
- Started with a clean DB.
- Checked out really old code that marks tasks as dupes using comments.
- Made a bunch of tasks and closed some as dupes. Made a bunch of additional comments.
- Checked out D10427 and did a `storage upgrade`.
- Made a bunch more new tasks and dupes.
- Snapshotted DB.
- Ran migration repeatedly until all expected edges showed up in the `phabricator_maniphest.edge`table.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T12234
Differential Revision: https://secure.phabricator.com/D18037
