Implement all field edit interfaces on the custom field schema

Summary:
Moves the revision edit controller to be completely schema-driven.

Depends on D810.

Test Plan: Edited revisions. Entered intentionally invalid values to trigger
error conditions.
Reviewed By: jungejason
Reviewers: jungejason, tuomaspelkonen, aran
CC: aran, jungejason, epriestley
Differential Revision: 810