re-arranged methods (#13)
added test stubs for model related methods (#13)
added test stub (#13)
added comments (#13)
implemented tests (#13)
added test (#13)
implemented some of the model methods (#13)
fixed column case (#13)
implemented deleteModel() (#13)
activated strict default graph behavior (default graph contains only triples that are not assigned to any graph) (#13)
changed test SPARQL queries to explicitly define the graph for selection (#13)