Provide VTD index where possible during import

[twagoo]

Where field value is determined in logic, pass the vtd index where applicable. This is helpful for curation.

[twagoo]

adding VTD context via an extra parameter to the addDocField* methods of CMDIData cannot be implemented in a trivial way, since the importer first collects all values per facet (FacetProcessor.processFacets()) and only then consolidates these into a field. The values can be derived from any number of paths in the source document so there is no straightforward relation between value and origin at the moment of storage.