Added calculator for computing electrostatic interaction using a traditional Ewald summation.
Properties include forces, stresses, Hessian, non-affine forces and elastic constants.
Furthermore additional parameters for the cg solver in get_non_affine_elastic_constants() are added
Added calculator for computing electrostatic interaction using a traditional Ewald summation. Properties include forces, stresses, Hessian, non-affine forces and elastic constants. Furthermore additional parameters for the cg solver in get_non_affine_elastic_constants() are added