re-think text_type
Current text_types are a mixture of relation (commentary, etc.) and and form of the text (prose, poem, translation).
Can we find a better representation?
Text relations are now PC67_refers_to with P67.1_has_type.
Current combinations of relation e.g. is_version_of and text_type need to be converted into the new system of relations.
Edited by Robert Casties