Move GUI unit tests to cpp files

Tests/UnitTests/GUI/TestAxesItems.cpp

Tests/UnitTests/GUI/TestComboProperty.cpp

Tests/UnitTests/GUI/TestComponentProxyModel.cpp

Tests/UnitTests/GUI/TestComponentUtils.cpp

Tests/UnitTests/GUI/TestCsvImportAssistant.cpp

Tests/UnitTests/GUI/TestDataItemViews.cpp

Tests/UnitTests/GUI/TestDataItems.cpp

Tests/UnitTests/GUI/TestDetectorItems.cpp

Tests/UnitTests/GUI/TestExternalProperty.cpp

Tests/UnitTests/GUI/TestFTDistributionItems.cpp

Tests/UnitTests/GUI/TestFitParameterModel.cpp

Tests/UnitTests/GUI/TestFormFactorItems.cpp

Tests/UnitTests/GUI/TestGUI.cpp

Tests/UnitTests/GUI/TestGUICoreObjectCorrespondence.cpp

Tests/UnitTests/GUI/TestGUIHelpers.cpp

Tests/UnitTests/GUI/TestGroupItem.cpp

Tests/UnitTests/GUI/TestLayerItems.cpp

Tests/UnitTests/GUI/TestLayerRoughnessItems.cpp

Tests/UnitTests/GUI/TestLinkInstrument.cpp

Tests/UnitTests/GUI/TestMapperCases.cpp