Adding QC functionality based on voxel intensity distributions

[tknijnen]

To identify outlier FoVs, we would like to add an additional QC metric which is based on the distribution of the intensities of voxels in the FoV for a particular channel. We want to compute:

1. a vector with the overall distribution of intensity values (across all three dimensions) and
2. a scalar representing the entropy of this distribution.

Outliers can then be detected by comparing this vector and/or this scalar across a group of FoV, and calculate which ones are far away from the bulk of FoVs.