Supporting more key fields in Import-ArticleFromXml

[cnEUL]

The Import-ArticleXml function should also accept ID, UDI and Barcode as key field.
Here preferably the ArtNummer, if this is not available, then the Barcode field, the UID and then the ID. In the case of the ID, a switch should allow this, which switches off the ID assignment in this case in the SQL server during the import. This option is only useful with an empty article table.