Rewrite triangle strip generation in the Blender exporter

Rewrite triangle strip generation in the Blender exporter

The old algorithm had many of the right ideas but was too clever by half
and consequently very complex.  Use a simpler score-based algorithm
developed by Tom Forsyth.  Also reorder vertices to make memory accesses
to them occur in a more linear fashion.

Options related to cache optimization were removed since there's
no good reason not to optimize.