Delete class CalibrationMeasurement and add class CalibrationRequest:
the ReferencePoint must be linked by the Request, not by each
Measurement of the Request.
Adapt ReferencePoint to link a CalibrationRequest instead of a
CalibrationMeasurement.
Request:
- Destructor is now virtual to allow polymorphism.
- Reactivate tests on get_measurements() and set_measurements().
Matteo Cypriani