Make ParameterSet store covariance as optional instead of pointer

This should have the advantage of it being local to the class, rather than a heap allocation that the client has to perform and pass to ParameterSet.

Core/src/Material/SurfaceMaterialMapper.cpp

@@ -10,10 +10,10 @@
 // SurfaceMaterialMapper.cpp, Acts project
 ///////////////////////////////////////////////////////////////////
 
+#include "Acts/Material/SurfaceMaterialMapper.hpp"
 #include "Acts/EventData/NeutralParameters.hpp"
 #include "Acts/Material/BinnedSurfaceMaterial.hpp"
 #include "Acts/Material/ProtoSurfaceMaterial.hpp"
-#include "Acts/Material/SurfaceMaterialMapper.hpp"
 #include "Acts/Propagator/ActionList.hpp"
 #include "Acts/Propagator/Navigator.hpp"
 #include "Acts/Propagator/Propagator.hpp"