Orientation change histogram (suggestion)

Hi,

I really like the additional visualizations in 3D Class in v4, and I wonder whether some analogous improvements would be helpful for refinement jobs.

Specifically, for NU & homogeneous refinement, I wonder if adding a histogram of per iteration particle orientation & offset changes (as for local refinement) would be useful.

This would be helpful I think for assessing convergence, particularly in cases of pseudosymmetry, where the FSC improvement criterion is not always reliable.

Cheers
Oli