Big update to the SPARQL support modules.

* [BAG,DBPEDIA,SC] Updates due to changes in SPARQL support modules.
* [ORDSET_EXT,SC] Removed.
* [PAIR_EXT,ROW_EXT,SC] New modules, based on predicates from ORDSET_EXT.
* [ROW_EXT,NEW] Rewrote rows_to_lists/2; andded rows_to_ord_set/2.
* [SPARQL,SC] Split into several modules: DB, BUILD.
* [SPARQL_BUILD,DOC] Documented several predicates.
* [SPARQL_BUILD,SC] Simplified several predicates.
* [SPARQL_DB,NEW] Rewrote the SPARQL DB, using library persistency.
* [SPARQL_WEB,SC] Cleanup. Still a lot to do here.