GROMACS

The final goal is to have every module manage its own input parameters, but on the way to there it is useful to split up t_inputrec in sub-structs. This can be done gradually by placing them into t_inputrec. These new structs should probably have in definition initialization.

The most needed sub-struct are for Van der Waals and electrostatics. The question is how these should be named, e.g.:
VanderwaalsParameters
ElectrostaticsParameters or CoulombParameters