Angles Da were not averaged correctly.

A circular average is needed. Still some problems with averaging. Perhaps I should average the diffusion tensors?
Added GetDiffFrom2DCovariance.

GetDiffFrom2DTensor[2Dcovar] returns {Dx,Dy,Dalpha} from the 2D covariance matrix.
Also changed all conversion to use N (for speed).
Angles currently averaged through tensors.

The circular average still had some problems
Playing around with various normality testing options
Fighting memory leaks in GetDiffusionInBinByMiddlePoint
Imporved EstimateDiffusionError, SaveDiffusions and added EstimateDiffusionErrorAndSave

SaveDiffusions now saves {"Diffusions"->..., "Metadata"->, "RawSteps"->...} structures directly.
Also changed so that it save to nonempty dirs by default.
EstimateDiffusionErrorAndSave now works flawlessly