Started work on debug tools for RDF(S) materialization.

* [RDF_DATATYPE,EXT] Allow names i.o. IRIs for standard XML datatypes.
* [RDF_MAT,SC] Improvements to argument order (`maplist` support).
* [RDF_MAT,EXT] Regimes are no longer applied transitively.
* [RDF_MAT,DEB] Use module `deb_ext` for debugging.
* [RDF_WEB,EXT] Markup generation for rdf_graphs_web/1 was outdated: added caption.