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.

• 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.