Various changes while getting the IOTW working again...

* [ASSOC_EXT,FIX] Type caused variables to not match.
* [DCG_MULTI,FIX] Wrong options were used inb dcg_multi1//5 (before meta_options/3).
* [DEV_SERVER,DEB] Use of custom HTPP dispatch predicate allows for easier debugging.
* [META_EXT,SC] Removed unused module import.
* [OAEI,FIX] Added missing module import.
* [ORDSET_EXT,NEW] Added equivalence_sets_to_number_of_equivalence_pairs/2. This was used in several locations.
* [RDF_GRAPH,FIX,SC] Placed the unit test code in a separate module. This fixes the strange problem that the module prefix was required even for importing modules.
* [RDF_MAT,EXT] Minor alterations so as to allow for multiple entailment regimes. Now completely done yet, what if the same entailment rule belongs to several regimes?
* [RDF_MAT,EXT] Added entailment regime `none`.
* [XML_DOM,FIX] The SVG namespace was not asserted, causing the injection of JS in SVG to fail.
* [XSD,FIX] Canonizing graphs did not work due to an atom/codes mismatch.
* [XSD,EXT] Added the datatype covered by module XSD? check to canonizing graphs.
* [XSD,DOC] Added documentation for canonizing graphs.