add new mfront model for clays

Hello, I would like to merge this model that is being implemented in MFront at BGE TEC by Miguel. I would like you please to help me through the process. Right now i just dropped the model into MaterialLib/SolidModels/MFront. I still have to make a CTest and add the jupyter tests too. By now I would like to know which files i should edit in order for ogs to know that the model exists. Regards, Eric