ENH: removing confusing default template in ImageLayer

Code/Visualization/otbImageLayer.h

Code/Visualization/otbStandardImageViewer.h

Testing/Code/Visualization/otbImageLayerGeneratorNew.cxx

Testing/Code/Visualization/otbImageLayerGeneratorScalar.cxx

Testing/Code/Visualization/otbImageLayerGeneratorVector.cxx

Testing/Code/Visualization/otbImageLayerNew.cxx

.../Visualization/otbImageLayerRenderingModelSingleLayer.cxx

Testing/Code/Visualization/otbImageLayerScalar.cxx

Testing/Code/Visualization/otbImageLayerVector.cxx

.../Code/Visualization/otbImageViewerEndToEndSingleLayer.cxx

...ng/Code/Visualization/otbImageViewerEndToEndTwoLayers.cxx

...ode/Visualization/otbPixelDescriptionModelSingleLayer.cxx