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