replace textual definition of distribution parameter by enum

Core/Export/PyFmt2.cpp

Core/Export/SimulationToPython.cpp

Core/Simulation/DepthProbeSimulation.cpp

Core/Simulation/ISimulation.cpp

Core/Simulation/ISimulation.h

Core/Simulation/OffSpecularSimulation.cpp

Core/Simulation/SpecularSimulation.cpp

Core/Simulation/StandardSimulations.cpp

Examples/scatter2d/BeamDivergence.py

Examples/varia/DepthProbe.py

GUI/coregui/Models/BeamDistributionItem.cpp

GUI/coregui/Models/BeamDistributionItem.h

GUI/coregui/Models/InstrumentItems.cpp

GUI/coregui/Models/TransformFromDomain.cpp

GUI/coregui/Models/TransformToDomain.cpp

GUI/coregui/Models/TransformToDomain.h

Param/Distrib/DistributionHandler.cpp

Param/Distrib/DistributionHandler.h

Param/Distrib/ParameterDistribution.cpp

Param/Distrib/ParameterDistribution.h