[pyramid] add routes /{eid} and /{etype}/{eid} to return RDF when rdf mimetype in Accept HTTP headers

* simplify pyramid/resources.py by making the classmethod that returns a closure
  a simple function and removing the EntityResource and ETYpeResource classes
  that are barely used
* replace predicate MatchIsETypePredicate with MatchIsETypeAndEIDPredicate

Team: famarger, schabot, nchauvat, fferry, ethieblin