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

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!