replace unnecessary stdi::string constructors

Core/Instrument/OutputData.h

Fit/Kernel/Parameters.cpp

Fit/Minimizer/MinimizerCatalogue.cpp

Fit/Minimizer/MinimizerOptions.cpp

Fit/Minimizer/TestMinimizer.cpp

Fit/RootAdapter/GeneticMinimizer.cpp

Fit/RootAdapter/RootMinimizerAdapter.cpp

Fit/Tools/MinimizerUtils.cpp

Tests/UnitTests/Core/Other/OrderedMapTest.cpp

Tests/UnitTests/Fit/StringUtilsTest.cpp

Tests/UnitTests/GUI/TestCsvImportData.cpp

Tests/UnitTests/GUI/TestScientificSpinBox.cpp