Implement more Differential fields on ApplicationTransaction/CustomField

Summary:
Ref T2222. Ref T3886. Gets the storage-based fields working.

This requires future changes to actually do anything, all this code is inactive.

Test Plan: {F118863}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3886, T2222

Differential Revision: https://secure.phabricator.com/D8357