Influence & Refactoring

* Adds support for influence (passes all the round trip tests for that)
* I've been doing a bit of refactoring:

I now handle all prov predicates regardless of the type of the subject, which means that ttl containing only 'ex:a2 prov:wasInfluencedBy ex:a1 .' can now be parsed. Before, this would be skipped as the type was unknown, and could not be inferred accurately from the ontology (wasInfluencedBy can apply to entity, activity, or agent).

This makes the parsing a little more lax, but I think this is a good thing :)