Migrate Project workboard to modular transactions

Summary: This was interesting, because there were a mix of callsites using transactions and others that just set the property on the Project object. I made everything consistent in using transactions to change this property. I also found an implementation of getTitle() that I don't think is ever being invoked since shouldHide() is returning true, but I migrated it anyway.

Test Plan: Unit tests pass + enabling/disabling workboards (and importing).

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D18004