Use `org-entry-*-multivalued-property` functions to handle vCard properties with multiple values

[flexibeast]

Adonay "adfeno" Felipe Nogueira suggested using the org-entry-*-multivalued-property functions to handle vCard properties with multiple values. These functions have been available since at least 2008, so it's reasonable to make use of them.

All three vCard specs specify that the EMAIL vCard property should only have one value (4.0, 3.0, 2.1). Thus, multiple email values for an Org EMAIL* property - including those specified via the EMAIL*+ syntax - should be split into distinct vCard EMAIL properties.