- Better HBase driver (adds filter)

- Remove hardcoded paths in HBase driver

- Remove useless QIRReductor class

translates the QIR tree to an executable QIR tree by detecting where to
execute the query parts. The evaluation then calls the appropriate visitor for
the evaluation of the different parts
- Create package qir.visitor, and reorganization of files

- Remove useless operators
- Minor improvments in GreedyReduceVisitor

- Table name of QIRTable now a QIRNode
- Fix toString for QIRString

- Remove old hack in PostgreSQL driver
- Rename QIRSelect in QIRFilter to avoid confusions with SQL's select

- Minor fixes

- Better toString for QIRLambda
- Throw exception in case of error in execution of query