I've moved the thumbnails around many times over this project
and hopefully it doesn't happen too many more. Once the database has
tens of thousands of items, the thumbnails start to become the biggest
headache on the disk. Backing up, restoring, and sharding files per
directory are slower and more effortful with separate files. In the db
means the db is a larger file, but this is disk space that was already
getting used anyway. Now it's simpler and has atomic transactions.
