RDF serialization of xrm mapping itself

[mchlrch]

Adding the possiblity to serialize (parts of) an xrm mapping (everything: source, vocab, mapping, dialect, ...) as RDF.

This improves hackability and unlocks possibilities for toolchain improvements outside of the xrm editor, for example:

• Deriving shapes from maps Derive shapes from maps #125 outside of XRM editor itself, eg. by means of SPARQL construct, N3 or other suitable ways
• Re-use of logical-source definitions, eg. XPath expression sanity checks, provenance info
• Re-use of IRI template
• Re-use of vocabulary definitions, eg. for ontology management request or proposals

This enables to re-use all information from an xrm mapping project, regardless of mapping output (eg. also for CSVW) and also for information, that is currently not contained in the generated mapping file.

We probably want to use quads, in order to be able to state the provenance back to the mapping files.