Summary: Ref T418. Moves data from the Maniphest-specific table to the general one. This patch is a bit gross, but mostly about getting the reads and writes aimed correctly. Future patches will clean things up.
Test Plan: Migrated data across formats. Verified it survied the migration. Viewed and edited tasks' custom fields.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T418
Differential Revision: https://secure.phabricator.com/D6999
