STYLE: renaming MetaDataKey static const string

Code/Common/otbVectorData.txx

Code/IO/otbGDALImageIO.cxx

Code/IO/otbImageBase.cxx

Code/IO/otbImageFileReader.txx

Code/IO/otbKMLVectorDataIO.txx

Code/IO/otbMetaDataKey.cxx

Code/IO/otbMetaDataKey.h

Code/IO/otbSHPVectorDataIO.txx

Code/Projections/otbOrthoRectificationFilter.txx

Code/Projections/otbVectorDataProjectionFilter.txx

Testing/Code/IO/otbOSSIMImageMetaDataReaderTest.cxx

Testing/Code/IO/otbVectorDataFileGeoReaderWriter.cxx

Testing/Code/Projections/otbSensorImageToCarto.cxx