added notes during Claus' review
minor updates on views.sparqlify

- removed and updated some comments
- removed leading + in SML addition
- no changes of the semantics of the mappings
minor changes on Pinpointer and ShortUri
introduced Triples instead of Statements

- the QualityAssessment instance now gives a Triple object to the
  registered metrics instead of a heavyweight Statement instance
updated and fixed ShortUri metric
added HttpUri metric