Removed the now unnecessary MatResponseForm. Material routines always return the reduced version. The full version can be constructed by the caller, whenever it is necessary (which is rare). See StructuralMaterial::giveFullSymMatrixForm and StructuralMaterial::giveFullSymVectorForm
Removed unnecessary overloading of giveCharacteristicMatrix in fluid material models.
Added missing changes to python bindings.
Removed unnecessary giveCharacteristic*** from Material (no need to have a common interface between different classes of materials)
Renamed StructuralMaterial::giveCharacteristicMatrix into the more suitable "giveStiffnessMatrix", as it always must be.