support all fields for ADR property

[equaeghe]

Currently, it does not seems to set a Post Office Box or Extended Address part of an ADR property. These address parts, although probably the least common, do come up quite often. For example, in the Netherlands, it is typical for companies and institutes to have a Post Office Box.

The necessary modification would be to add the necessary fields to the interface. A judgment that this would make the interface too heavy would imply that some redesign is necessary (which may not be trivial).