Additional complex testcases for SPARQL

[Ritvik1712]

In response to issue#115, we are adding few additional complex test cases that address various aspects of SPARQL.

[lambdamusic]

The test https://github.com/lambdamusic/Ontospy/blob/master/ontospy/tests/test_sparql.py simply aims at verifying a SPARQL connection.
So not sure why complex testcases are needed. It doesn't matter how complex the query is, that complexity all lies outside Ontospy and hence nothing worth testing I'd say.