Summary:
Fixes T6013. Old image macros/memes never had the file edge written.
We also never wrote file edges for audio.
Finally, the meme controller didn't allow public access.
Write edges for images and audio, perform a migration to populate the historic ones, and make the Editor keep them up to date going forward.
Test Plan:
- Updated image, saw new image attach and old image detach.
- Updated audio, saw new audio attach and old audio detach.
- Ran migration.
- Viewed memes as a logged-out user.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T6013
Differential Revision: https://secure.phabricator.com/D10411
