Summary: Ref T418. Maniphest has an obsolete class-based field selector. Replace it with CustomField-based selectors, which use the nice config UI and are generally way easier to use.
Test Plan: Added custom fields; edited and viewed custom fields on tasks. Everything worked as expected.
Reviewed By: btrahan
Maniphest Tasks: T418
Differential Revision: https://secure.phabricator.com/D6998