This MR adds:
- The base TrackerDeserializer object and constructors, allowing to create a cursor from an input stream plus a namespaces manager.
- An intermediate TrackerDeserializerRdf abstract class to help with RDF formats and make these consistent.
- A TrackerDeserializerTurtle (refactored from TrackerTurtleReader) that converts Turtle into a cursor. All places that parse Turtle have been updated to use this.
- Some code to handle Trig in addition to Turtle, within the same object.