Regroup parameters to other group

The parameters Problem.PoissonRatio, Problem.SandGrainRoughness, Problem.UsePrimaryVariableSwitch and Problem.YoungsModulus should not be part of the Problem group as the Problem group should only contain parameters of the FVProblem and model agnostic problem base classes. Therefore, the four parameters should be regrouped. Once regrouped, the parameter file should be updated accordingly for these parameters.