Support for LDTab Profiles

[ckindermann]

LDTab includes a variety of features. To make LDTab more accessible and reduce the initial complexity for new users, we could provide selected features in dedicated profiles. We have been thinking about:

• LDTab-RDF: restricting the statement table to the columns subject, predicate, object, datatype, and annotation. This effectively reduces LDTab to a concrete syntax for RDF/OWL,
• LDTab-Edit: extending LDTab-RDF with the columns assertion and retraction to maintain different versions of an RDF graph/OWL ontology,
• LDTab-Quad: extending LDTab-RDF with the column graph to maintain multiple graphs,
• LDTab-Full: all of the above.

The default should be LDTab-Full. Different profiles should be selected using the option --profile. The commands import and export should infer the correct profile.