Big rewrite of RDF literal codebase.

* [ATOM_EXT,NEW] Added atomic_atom/[2,3] mapping atoms, code lists, numbers, strings to atoms.
* [CODES_EXT,EXT] Add string to code lists mapping.
* [RDF_BOOLEAN,RDF_DATETIME,RDF_STRING,NEW] New module with shortcut/wrapper predicates for triple with literals with boolean, date, dateTime, and string datatypes.
* [RDF_DATATYPE,NEW] Full rewrite of RDF datatype assertion support: reusing the new RDF_LITERAL.
* [RDF_LANGUAGE_TAGGED_STRING,NEW] New module supporting this literal type, introduced in RDF 1.1.
* [RDF_LITERAL,NEW] Full rewrite of RDF literal support. Now conforms to RDF 1.1.
* [RDF_PLAIN_LITERAL,RDF_SIMPLE_LITERAL,RDF_TYPED_LITERAL,NEW] Complete rewrite of RDF literal legacy (RDF 1.0) support.
* [RDFS_LABEL_EXT,NEW] Full rewrite of RDF label support, reusing the new RDF literal and RDF datatype, supporting RDF 1.1.