Add `WorkbenchImport` model
Created by: teddywing
A new model that represents a batched import. The zip archive attached
to this record will contain one or more datasets. A Referential will
be created for each dataset in the zip, and that sub-dataset will be
scheduled for a Netex import (only handling Netex imports at the
moment).
The model is currently empty but I'm committing it now so it can be used by others on the team.
Refs #3507