SDMN — XML Namespace URI needs updating

The XML namespace URI of the original SDMN submission uses a dated version stamp, which if changed with each revision could lead to model interchange issues, i.e. different tools supporting different versions with incompatible XML namespaces (see also SCE-117).

In addition, the following sentence about imports was accidentally copied from DMN is invalid for SDMN:

SDMN files MAY import non-SDMN files (such as XSDs and PMMLs) if the contained elements use external
definitions.