Make all revision status readers explicitly read modern or legacy status

Summary: Ref T2543. All writers now write modern statuses. Make all readers explicit about whether they are reading modern or legacy statuses, so I can swap the storage format.

Test Plan:

• Grepped for getStatus(), scanned the list. Other applications have methods with this name so it's possible I missed something.
• Browed around, changed revision statuses.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18417