#19 support clone() for data objects

I have a few places where either I:
(1) have to return a VIM data object to a caller and want to give him a defensive copy rather than a reference to my internal state.
or
(2) have a VIM data object that I want to duplicate but don't know the real type. E.g., I want to add a second NIC to a VM, but don't know which subclass
of VirtualEthernetCard is the best to use for the guest/hypervisor combination. So I'd like to duplicate his first NIC, change the unit number, and
pass it right back into VM.reconfigure.

So it'd be great if DynamicData implemented Cloneable, and used the existing DeepCopier to implement clone().