BNode handling

Whenever I encounter a BNode, I convert it into a QName with our prov toolbox namespace. There are then a couple of checks:
* When creating an influence, if the ID is a BNode and is not referenced by any other triples, it is nullified.
* Once all parsing is done, it goes through all the objects. If they have a BNode ID, it nullifies the ID if the BNode is not referenced by any other triples.