Subtle, but significant camera changes:

- Added 3rd person camera lateral offset that shows your lateral momentum.  Although subtle, this does help significantly in my experience after you get used to it.

- Added lateral camera offset magnitude in settings to allow for some user testing.

- VERY subtle: added variable pitch differential to the third person camera based on how much vertical velocity there is perpendicular to the forward vector.  Not sure about this yet but it seems to feel good.  Let me know if you have any issues with up/down turns and vertical loops; this could be the cause.  it feels good to me.

Although these changes are visually subtle, they make for a significant gameplay improvement, and the camera code has been refactored, which will allow for easier changes moving forward.

Check out powersliding!  It's much easier to tell how things are moving now with the lateral camera offset.

More tweaks coming...

(Also fixed an issue preventing certain block structures from spawning when using performance blocks.)