rdf normalization identical to gromacs (fixes issue 84)
rdf normalization identical to gromacs (fixes issue 84)

using exact shell volumes (difference of spheres) and n*n/2 instead n*(n-1)/2 for same particle type

junghans/csg,junghans/csg,junghans/csg,MrTheodor/csg,junghans/csg,votca/csg,MrTheodor/csg,MrTheodor/csg,junghans/csg,votca/csg,votca/csg,junghans/csg,votca/csg,MrTheodor/csg,MrTheodor/csg