Make Dashboards and Panels Flaggable
Summary: Ref T8888, makes these two objects flaggable.
Test Plan: Set Flag, See Flag.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T8888
Differential Revision: https://secure.phabricator.com/D13652