- lots of experimenting trying to find out why large models are garbled:
 * answer: webgl does not support indices beyond 65535 (uInt16), except
if specific extension is available
 * possible workarounds : on most browsers/platforms, one can use uInt32
index buffers, OR need to split into chunk (see ctm parser) OR do not use indices
 * various related tweaks and experiments
 * for now de-activated four component colors

- added "pseudo" progress reporting at various stages, so it does not look like
the parser crashed