Routines for the qualitative evaluation of slope parameters.

**slope image** computes an image of sum squared image gradients normalised
to image noise and places it on the image stack for view in the Imcal Tool*Tv*..

**scat plot** produces a scatter image of multi-dimensional normalised gradient verses
grey level (for current **Sequence Tool***Tv* image).

**grad model** produces a image of computed probability densities
for multi-dimensional normalised gradient verses
grey level (for current **Sequence Tool***Tv* image).

root 2017-11-20