Maniphest - load subscribers in getApplicationTransactionsObject

Summary: Fixes T6734. This is a very generic fix, which basically attaches the subscribers if necessary. This seems like a good idea given there's some crazy generic code doing this sort of thing? This would end up being a new pattern for these types of objects that may be loaded by a general object query but then get some editor action against them.

Test Plan: I can't actually reproduce this in my sandbox so I'll verify live again.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6734

Differential Revision: https://secure.phabricator.com/D10976