Include owners packages in the MailableFunction datasource
Summary:
Ref T13151. See PHI684. Currently, the `MailableFunction` datasource does not include Owners packages, but they are valid subscribers and the `Mailable` datasource includes them.
Include them in the `MailableFunction` datasource, too.
Test Plan: Searched for revisions with particular package subscribers, got expected results in the UI (tokenizer knew about packages) and response.
Reviewers: amckinley, jmeador
Reviewed By: jmeador
Maniphest Tasks: T13151
Differential Revision: https://secure.phabricator.com/D19476