Make markers in `rdf-macro` configurable

[TobiasNx]

The markers should be configurable, came up in #589 and is currently not workable with fix due to #656:

metafacture-core/metafacture-linkeddata/src/main/java/org/metafacture/linkeddata/RdfMacroPipe.java

Lines 38 to 42 in 1a5e003

	public static final char REFERENCE_MARKER = '*';
	public static final char LANGUAGE_MARKER = '$';
	public static final String RDF_REFERENCE = "~rdf:resource";
	public static final String RDF_ABOUT = "~rdf:about";
	public static final String XML_LANG = "~xml:lang";

[TobiasNx]

Done with: #658