R1:48059265f37a

Use CustomFields to power Conduit auxiliary dictionaries

Summary: Ref T2222. Moves this Conduit stuff over.

Test Plan: Made Conduit calls, saw data in results.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8469