[BL] Refactored getFileExtension().

Applications/DataExplorer/VtkVis/VtkVisImageItem.cpp

Applications/DataExplorer/VtkVis/VtkVisPointSetItem.cpp

Applications/FileIO/AsciiRasterInterface.cpp

Applications/FileIO/SWMM/SWMMInterface.cpp

Applications/FileIO/TetGenInterface.cpp

Applications/FileIO/readGeometryFromFile.cpp

Applications/FileIO/writeGeometryToFile.cpp

Applications/Utils/MeshEdit/createLayeredMeshFromRasters.cpp

Applications/Utils/MeshEdit/moveMeshNodes.cpp

...ications/Utils/MeshGeoTools/createIntermediateRasters.cpp

Applications/Utils/PostProcessing/postLIE.cpp

Applications/Utils/SWMMConverter/SWMMConverter.cpp

BaseLib/FileTools.cpp

MeshLib/IO/VtkIO/VtuInterface.cpp

MeshLib/IO/readMeshFromFile.cpp

MeshLib/IO/writeMeshToFile.cpp

Tests/BaseLib/TestFilePathStringManipulation.cpp

Tests/FileIO/TestTetGenInterface.cpp