Make DV_ORDINAL.rubric a DV_CODED_TEXT; type attribute not needed

If DV_ORDINAL rubric (values like "low", "medium", "high"
etc) and type (values like "pain", "reflex reaction" etc) are to
be interoperable, they need to incorporate language, and to be
coded.

The type attribute, in which it was thought that the category of
values would go (e.g. "pain", "protein concentration" etc) to
ensure that even if the same symbols were used (e.g. "++"), they
could not be mixed up.

A better name for the rubric attribute would be "symbol".