Update and extend Cromer-Mann parameters for calculating scattering intensities

For computing the form factor we use an heuristic fit done by Cromer and Mann. They conducted Hartree-Fock simulations and obtained these parameters that we store in src/maicos/share/sfactor.dat. The number of digits is not very large and we should extend this similar to what the GROMACS project has in their current version.

Also, we should add the parameters for charged elements (ions) which are missing as well in the GROMACS code. If we add the ions we have to update the type-to-element mapping in src/maicos/share/atomtypes.dat, because currently we map ion types to their neutral elements, which is questionable. All values are reported online as PDF and HTML. See Table 6.1.1.4.

Basically, I have these tasks in mind

1. Rename sfactor.dat -> scatteringfactors.dat to have a better name
2. Update values according to GROMACS version
3. Add values for ions
4. Update reference in header accordingly