Changed handling of DoseGridScaling: before this commit, rescaleSlope was set to the DoseGridScaling value if rescale* tags weren't present AND in the case of a dose. This caused issues in dose files where all three tags (DoseGridScaling, RescaleSlope and RescaleIntercept) were present, which previously led to the DoseGridScaling tag to be ignored. Now, the rescale* tags are *ignored* in dose files and DoseGridScaling is always taken into account.