Drive Maniphest statuses with internal pseudo-configuration

Summary: Ref T1812. Without actually exposing configuration, this moves all status information into a config-like chunk of data which can later be exposed to human editors.

Test Plan:
  - Made a bunch of status changes.
  - Merged duplicates.
  - Created task.
  - Viewed feed, transaction record, etc.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1812

Differential Revision: https://secure.phabricator.com/D8582