Summary:
Currently, the author of an image macro is read from the attached file. This is messy and necessitates a join, and is not always correct. Instead, store the data when the macro is created.
This lays the groundwork for generalizing ApplicationSearch here. Ref T2625.
Test Plan: Migrated existing macros, created a new macro, checked web UI.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2625
Differential Revision: https://secure.phabricator.com/D6071
