The trouble with this is, if they aren't included in the allowed_extensions, then we not only disallow them from upload, but we forbid them from being included in the DB (syncChildren will omit them). It's a potential usability and security risk to have an app_category with extensions that are disallowed in this way.

We could either do this, and document the above caveat, but I prefer to omit them entirely and document how users can re-add these back in.