Aspera connector needs to handle Files with 'folderish' facet

Consider a doctype like this one:

    <doctype name="ComplexFile" extends="File">
      <facet name="Folderish"/>
    </doctype>

The doctype has the 'file' and 'files' schemas and is folderish. Clients need to be able to download blob attachments (primarily) and attachments of children (secondarily)

Refactor the Aspera connector to
1. enable download and upload of blobs attached to a document of this type
2. enable download and upload of blobs attached to children of a document of this type

Point 1 takes priority.

See similar Nuxeo Drive issues (linked)