Implementing CKAN API support.

* [CKAN,NEW] New module implementing CKAN API support.
* [HTML,HTTP,SC] Separated HTTP- from HTML-specific predicates and catch methods.
* [HTML_TABLE,NEW] Added DCH/DSL implementation of html_table/3.
* [JSON_EXT,NEW] Added json_rows/2 for converting table-like JSON results to pure Prolog lists (e.g. input to html_table/3).
* [XML_TO_RDF,FIX] Added missing module imports.
* [URI_EXT,NEW] Added uri_path/2 for building URI paths out of lists of atomic terms, skipping variables.