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