#552 Detector non-linearity and reciprocity failure

A basic method to apply any desired non-linearity on an Image has been included to begin with. The non-linearity can be specified by a LookupTable or as a function, possibly with parameters, that can act on NumPy arrays. In addition, it also includes a feature to correct for reciprocity failure. A basic unit test to test these functionalities have also been built.
We do not have scipy as a dependency, so we cannot do this.  If you want to do this, it has to be in a try/except block, with the tests that use scipy only running if scipy is found.