Investigate and fix errors around slicing in our schema builder

[Kasdejong]

We seem to still have an issue around slicing in the schema builder.

• "Encountered an error while loading schema 'https://example.de/fhir/StructureDefinition/MyPractitioner': Failed to convert ElementDefinition at Practitioner in profile https://example.de/fhir/StructureDefinition/MyPractitioner: Encountered an invalid or incomplete slice at element 'Practitioner.gender', which cannot be understood by the validation."
• "Encountered an error while loading schema 'http://hl7.org/fhir/test/StructureDefinition/medstmt-ips': Failed to convert ElementDefinition at MedicationStatement.effective[x].extension in profile http://hl7.org/fhir/test/StructureDefinition/medstmt-ips: Encountered a slice that has no slice name."

[ewoutkramer]

It's not unlikely that these profiles are in fact incorrect ;-)