LibSoftGPU used to calculate the normal transformation based on the
model view transformation for every primitive, because that's when we
sent over the matrix. By making LibGL a bit smarter and only update the
matrices when they could have changed, we only need to calculate the
normal transformation once on every matrix update.
When viewing `Tuba.obj` in 3DFileViewer, this brings the percentage of
time spent in `FloatMatrix4x4::inverse()` down from 15% to 0%. :^)
