Add checksum calculation invariant (modulus 11) to CVR number

[jvitrifork]

• almost as done on http://build.fhir.org/ig/hl7au/au-fhir-base/StructureDefinition-au-hpii-definitions.html

• Algorithm is defined at https://da.wikipedia.org/wiki/Det_Centrale_Virksomhedsregister#CVR-nummer

[JesperKervin]

The header may trick me, but I think CVR is having checksum calculation invatiant modulus 11.

[jvitrifork]

@JesperKervin you're right. I don't know why I wrote '12'