PDME — allow "document type" to be the IdContext "kind"

The class "Document" is not necessarily a useful "object category" for name
scoping. Documents have
company-standard or even industry-standard "types", e.g. "structures model" or
"piping model", and those are the types of the "business objects" inside the
PDM. Company document naming conventions may focus on "document type". E.g.
"Geometric-model, 12345-1" and "Type3-load-analysis, 12345-1" may be unique
names for different DocumentMasters, whereas "DocumentMaster, 12345-1" doesn't
name anything. But "PartMaster, 12345-1" does, because "Part(Master)",
"Geometry-model" and "Type3-load-analysis" are the "business objects".