WIP revising diffraction apterture classes

benchmarks/DiffractionModelsBenchmark.cpp

include/ITAPropagationModels/Maekawa.h

include/ITAPropagationModels/Svensson.h

include/ITAPropagationModels/UTD.h

src/ITAPropagationModels/FilterEngine.cpp

src/ITAPropagationModels/Maekawa.cpp

src/ITAPropagationModels/Svensson.cpp

src/ITAPropagationModels/UTD.cpp

tests/FilterEngine/FilterEngineTest.cpp

tests/Maekawa/MaekawaTest.cpp

tests/Svensson/SvenssonTest.cpp

tests/UTD/UTDTest.cpp