There's no "standard" coordinate system, so the choice is arbitrary.
However, an examination of the Transporter mesh in Elite revealed
that the mesh was designed for a left-handed coordinate system. We
can compensate for that trivially in the Elite visualizer, but we
might as well match what they're doing. (The only change required
in the code is a couple of sign changes on the Z coordinate, and an
update to the rotation matrix.)
This also downsizes Matrix44 to Matrix33, exposes the rotation mode
enum, and adds a left-handed ZYX rotation mode.
This does mean that meshes that put the front at +Z will show their
backsides initially, since we're now oriented as if we're flying
the ships rather than facing them. I considered adding a 180-degree
Y rotation (with a tweak to the rotation matrix handedness to correct
the first rotation axis) to have them facing by default, but figured
that might be confusing since +Z is supposed to be away.
Anybody who really wants it to be the other way can trivially flip
the coordinates in their visualizer (negate xc/zc).
The Z coordinates in the visualization test project were flipped so
that the design is still facing the viewer at rotation (0,0,0).
