Notify users when an object they created gets awarded a token

Summary:
  - Publish feed/notification.
  - I think this is too lightweight for an email?
  - We don't tell them which token right now. Laziness? Or intentional aura of mystery?!
  - For tasks, notify both author and current owner.
  - Fixes T2562.

Test Plan: {F33187}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2562

Differential Revision: https://secure.phabricator.com/D5007