PIDS11 — using XML for traits and metadata

Since this representation of trait values in XML is fully-compliant at the
IDL level, it's not a functionality change.
The expression of trait metadata (so as to document the STRUCTURE of it) is
a functionality change but it is defensible as a fix, even to make to make
it possible for PIDS clients to validate dates - not just textual format but
the value domains at the basic and abstract datatypes.

I think we can all agree at this point that we need an operation on
IdentificationComponent called

get_trait_metatdata

and I feel strongly that it should use DTD notation. If we agree at this
level (please everyone - do you agree so far?), then I think the next
question is how to express basic and abstract types in the DTD.