Merge pull request #2856 from TomFischer/Improve_checkMPLProperties

MaterialLib/MPL/CheckMaterialSpatialDistributionMap.h

ProcessLib/ComponentTransport/ComponentTransportProcess.cpp

...ib/ComponentTransport/CreateComponentTransportProcess.cpp

ProcessLib/GroundwaterFlow/CreateGroundwaterFlowProcess.cpp

ProcessLib/GroundwaterFlow/GroundwaterFlowProcess.cpp

ProcessLib/HT/CreateHTProcess.cpp

ProcessLib/HT/HTProcess.cpp

ProcessLib/LiquidFlow/CreateLiquidFlowProcess.cpp

ProcessLib/LiquidFlow/LiquidFlowProcess.cpp

ProcessLib/RichardsFlow/CreateRichardsFlowProcess.cpp

...sLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp