Reorganize output management

CMakeLists.txt

src/CMakeLists.txt

src/language/algorithms/AcousticSolverAlgorithm.cpp

src/language/modules/SchemeModule.cpp

src/language/modules/VTKModule.cpp

src/language/modules/VTKModule.hpp

src/output/CMakeLists.txt

src/output/IWriter.hpp

src/output/NamedDiscreteFunction.hpp

src/output/OutputNamedItemValueSet.hpp

src/output/VTKWriter.cpp

src/output/VTKWriter.hpp

src/scheme/DiscreteFunctionDescriptorP0.hpp

src/scheme/DiscreteFunctionInterpoler.cpp

src/scheme/DiscreteFunctionP0.hpp

src/scheme/IDiscreteFunction.hpp

src/scheme/IDiscreteFunctionDescriptor.hpp

tests/CMakeLists.txt