Generic cleanup task.

* [ABNF2DCG,DEB] Rewrote the test pridicate using the unit test library.
* [SC] Removed many superfluous module imports.
* [FIX] Many fixes to dynamic/1 declarations, using term notation.
* [GRAPH_TRAVERSAL,DEB] Added debug statement for neighbor traversion.
* [SC] Removed meta-data modules about standards.
Generic updates to module structure.

* [SC] Replaced several low-level module imports of cowspeak by debug.
* [SC] Removed several superfluous module imports.
* [SC] Added several missing module imports.
* [BETWEENNESS,SC] New module for betweenness metric calculation.
* [DCG_GENERIC,SC] Removed dcg_debug//0.
* [DEV_SERVER,FIX] Added HTTP handler for plDoc documentation.
* [GRAPH_TRAVERSAL,SC] Cleanup of graph traversal methods traverse/[7,10].
* [GRAPH_TRAVERSAL,DEB] Use meta option for debug statements.
* [GRAPH_TRAVERSAL,SC] Use of default options outside of recursive loops (more efficient), using module OPTION_EXT.
* [LIST_EXT,GRAPH_GENERIC,SC] icompare/3 was defined twice.
* [MODEL_THEORY,XFN,DEB] Test predicates now use the unit testing infrastructure.
Updates for random RDF terms and RDF datasets.

* [RDF_DATASET,NEW] New module implementing RDF datasets, as defined in SPARQL 1.1.
* [RDF_READ,EXT] Distinguished rdf_random/5 in rdf_random_term/[2,3] and rdf_random_triple/4 (private).