when using an attenuation image, the sensitivity calculation can fail due to symmetries

[KrisThielemans]

At present, the symmetries used for the actual reconstruction and for the normalisation are assumed to be the same. However, when using an atten-image (via BinNormalisationFromAttenuationImage),this would depend on projectors used etc.

For instance, if the atten-image is shifted but the target image is not, the projector used for the mu-map needs to set symmetries off in its calculation, but projectors used for the reconstruction will not do that. Therefore during the sensitivity calculation the projector for the mu-map will be called with a RelatedViewgrams with all possible symmetries enabled. This will cause an error to be thrown

ForwardProjectByBin: forward_project called with incorrect related_viewgrams. Problem with symmetries!