Replace normalizers w/ calibrators (that have no calibration samples)?

[damellis]

We could model our current normalizers as calibrators that have no calibration processes / samples. We could even overload useCalibrator() to accept a function and create the Calibrator object internally.

This would mean removing the ability to use both a normalizer and a calibrator, but that might be a good thing. I'm not sure when you'd need both, and it seems confusing to provide them both without being able to explain when you'd use which.