DPROD11 — Support a direct dependency relationship between data products

See https://github.com/EKGF/dprod/issues/77
In my experience cataloging data products, it is often desirable to express a (input) dependency between data products, as supposed to express a (input) dependency of a data product on (other) datasets. So my request would be to have an objectproperty between two data products that declares that one data product uses the data from another data product (without having to specify which specific dataset).