Working on CKAN API and CKAN-to-RDF conversion.

* [CKAN,EXT] JSON<->PL conversions using json_object/1.
* [CKAN,EXT] Again added several predicates.
* [CKAN_TO_RDF,NEW] New module for converting CKAN sites to RDF.
* [DCG_CONTENT,NEW] Added capitalize//0.
* [DCG_GENERIC,NEW] Added dcg_copy//0.
* [JSON_EXT,SC] Cleanup of existing predicates.
* [JSON_EXT,NEW] Added json_boolean/2.
* [JSON_EXT,NEW] Added json_to_rdf/3 conversion.
* [CKAN,EXT] Added paginates/1 option to current_package_list_with_resources/4 (untested).
* [CKAN,EXT] Use http_open/3 i.o. http_post/4 for sending HTTP requests / handling HTTP replies. This allows us to retrieve the HTTP status code!
* [CKAN,FIX] Argument order of group_list/7.
* [CKAN,EXT] Process HTTP replies from CKAN using JSON<->PL conversion (using json_object/1).
Added several modules for specific CKAN deployments.
* [CKAN,EXT] Implemented deprecated parameter `page`.
Started a new initiative: automated conversion from Prolog terms to RDF triples. Only booleans and atoms for now...
This should replace the json_to_rdf conversion from module json_ext.
* [CKAN,NEW] Added package_show/3.
* [CKAN,EXT] Added JSON2PL conversion for resources and packages.
* [CKAN,FIX] The default value for the offset parameter is 1, not 0.
* [CKAN,EXT] Added deprecation support for license_list/2.
* [DATA_GOV_UK,SC] Simplified predicate.
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