Badges baked by backpack should be able to be uploaded into backpack

[fixes #912]
[fixes #966 ]

I had a hard time writing automated tests for this (and I've kinda started thinking that some of the automated controller testing introduces too much rigidity).

**Manual testing**:
1. Log in
2. Go to `/demo/ballertime`
3. Save the badge image from the first badge
4. Remove that badge from the backpack
5. Upload that badge back into the backpack
6. Badge should show up in the backpack without error.