DOC: change group of image list headers from OTBObjectList to OTBImageList

Modules/Core/ImageList/include/otbImageList.h

Modules/Core/ImageList/include/otbImageListSource.h

Modules/Core/ImageList/include/otbImageListToImageFilter.h

...re/ImageList/include/otbImageListToImageListApplyFilter.h

...es/Core/ImageList/include/otbImageListToImageListFilter.h

.../Core/ImageList/include/otbImageListToSingleImageFilter.h

.../Core/ImageList/include/otbImageListToVectorImageFilter.h

Modules/Core/ImageList/include/otbImageToImageListFilter.h

.../Core/ImageList/include/otbVectorImageToImageListFilter.h