Move read_ds_ebounds() from GCTAEventList to CTA support file and add ebounds() method to GCTAObservation.
Implement __itruediv__ and remove /=operator as SWIG seems not to handle correctly the new Python 3.x division logic.
Add Python unit tests for operators
Add __idiv__ operator for Python 2.x support, remove operator/=.
Implement division operators for Python 3.x.