[789-deprecate-content-of-globaldefinitions] Scalar -> double

FWI/src/ForwardModels/ForwardModelRed.cpp

FWI/src/Helper/FWIHelpers.hpp

FWI/src/Helper/NormCalculation.cpp

FWI/src/Observation/DGSeismogram.hpp

FWI/src/Observation/segy.h

TimeStepping/src/DGAssemble.cpp

TimeStepping/src/DGVAcousticAssembleCombined.cpp

TimeStepping/src/DGVAcousticMatrixAssembler.cpp

TimeStepping/src/DGVAcousticRHSAssembler.cpp