versions of the manifest.
group subscriptions not yet implemented, and reading of signatures
not yet implemented. Controls on group membership and pushing files
to groups not yet implemented. Group ciphers not yet implemented.
Some work on updating existing manifests, although some cascading
consequences need addressing (in particular checking if the file
associated with the old version of the manifest still needs to hang
about, and if so, whether its highest priority has changed).
Wrote function to store file to db iff it is not stored already,
and update the priority flag on the stored file.
Uses blobio to progressively load large blobs to make it friendly
on small memory systems.
