Simplify tarball storage interface

[billiegoose]

Finally figured out what the 'binarydb' is and why I can't find "where the tarball files are cached". They're stored in a 'level' (not even a levelup) database in the binarydb folder.

I don't think this is a good idea. I would much rather have a storage backend that was either agnostic abstract-blob-store or like registry-static.