Worker to add missing photo associations

[jvyden]

We can use the new Worker system to periodically check for new users, and then look for unattributed users in photo subjects.

So userA uploads a photo with userB, without userB being registered. userB gets tracked in the uploaded photo with a username (missing their GameUser association), and then userB registers. At this point, the uploaded photo still hasn't tracked their signup accordingly, so our worker runs and updates the photo to add the GameUser to the photo subject.