Change digit constants to character constants (BoundaryConditions)

src/cpu/VirtualFluidsCore/BoundaryConditions/BCFunction.cpp

...VirtualFluidsCore/BoundaryConditions/BoundaryConditions.h

...VirtualFluidsCore/BoundaryConditions/DensityBCAdapter.cpp

...ore/BoundaryConditions/HighViscosityNoSlipBCAlgorithm.cpp

...yConditions/MultiphaseNonReflectingOutflowBCAlgorithm.cpp

...uidsCore/BoundaryConditions/MultiphaseSlipBCAlgorithm.cpp

...dsCore/BoundaryConditions/MultiphaseVelocityBCAdapter.cpp

...Core/BoundaryConditions/MultiphaseVelocityBCAlgorithm.cpp

...irtualFluidsCore/BoundaryConditions/NoSlipBCAlgorithm.cpp

...re/BoundaryConditions/NonReflectingOutflowBCAlgorithm.cpp

...uidsCore/BoundaryConditions/RheologyNoSlipBCAlgorithm.cpp

...dsCore/BoundaryConditions/RheologyVelocityBCAlgorithm.cpp

...alFluidsCore/BoundaryConditions/SimpleSlipBCAlgorithm.cpp

...pu/VirtualFluidsCore/BoundaryConditions/SlipBCAdapter.cpp

.../VirtualFluidsCore/BoundaryConditions/SlipBCAlgorithm.cpp

...uidsCore/BoundaryConditions/ThinWallNoSlipBCAlgorithm.cpp

...dsCore/BoundaryConditions/ThixotropyNoSlipBCAlgorithm.cpp

...yConditions/ThixotropyNonReflectingOutflowBCAlgorithm.cpp

...Core/BoundaryConditions/ThixotropyVelocityBCAlgorithm.cpp

...ryConditions/ThixotropyVelocityWithDensityBCAlgorithm.cpp