Prepare for forward declarations in ISimulation

Core/Examples/StandardSimulations.cpp

Core/Export/SimulationToPython.cpp

Core/Fitting/SimDataPair.cpp

Core/Simulation/DepthProbeSimulation.cpp

Core/Simulation/GISASSimulation.cpp

Core/Simulation/ISimulation2D.cpp

Core/Simulation/ISimulation2D.h

Core/Simulation/OffSpecularSimulation.cpp

Core/Simulation/SpecularSimulation.cpp

GUI/Models/GUIObjectBuilder.cpp

GUI/Models/TransformToDomain.cpp

Tests/Performance/Core/Threading.cpp

Tests/Performance/Core/ThreadingComponents.cpp

Tests/Unit/Core/SpecularSimulationTest.cpp

auto/Wrap/doxygenDevice.i

auto/Wrap/libBornAgainDevice.py

auto/Wrap/libBornAgainDevice_wrap.cpp