[Property] Cannot append value of DType 'person'

Trying to append a value to a `Property` with `DTpype.person` the following error occurs:

```
prop = odml.Property(name="prop", value=["A Abraham", "B Barnes", "C Clark"], dtype=odml.DType.person
 prop.append("D Dickins")

ValueError: odml.Property.append: passed value data type does not match dtype!
```