to be used in the export. For purposes of development the default setting
in the UI is set to COPY, this is contrary to other default value for path_mode.
It may be appropriate to set the default UI setting to AUTO upon merging into
release code.
Added logging messages to export_x3d.py. The intent here is to extend the copy_set
mechanism to handle cases where the image file does not exist on disk at time of
export.
properly write the ImageTexture node even when there is no
explicit file name (as the case when image is read from a glTF file)
and save the image file to disk
