Merge branch 'u/pgee/DM-1067'
DM-1015 Simplifies GaussianFlux algorithm by using slots to calculate centroid and shape.

Remove the config options fixed, centroid, shape, and shapeFlag
Remove code from GaussianFlux.cc which is required to support the non-fixed option
Code is now equivalent to the previous setting fixed=True, centroid=current centroid slot
shape=current shape slot, shapeFlag=flag of current shape slot.

Now that the shapeFlag can cause GaussianFlux to fail, modify unit tests accordingly