R1:9ccef52d6c3f

Prevent awarding/revoking tokens when a task is locked

Summary: Ref T12335. Allows you to lock tasks to keep your precious tokens.

Test Plan:
- Awarded tokens to an unlocked task.
- Locked the task.
- Could no longer award/rescind tokens.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12335

Differential Revision: https://secure.phabricator.com/D17461