hack: patch LwjglRenderer to allow GL_DEPTH_STENCIL_ATTACHMENT (via depth in format Format.Depth24Stencil8)
DebugTextureViewer: better display of MatIds when less than 256 colors.
add shaders .frag to help debugging
DebugTexureViewer: missing change for MatId debugging
LBuffer: first working version using stencil buffer to limit light volume.