Attempt to make easier to print

Reduce overhang angle and make groove spaces taller and spaced farther
apart
Try an idler on a shaft that is on bearings

The idler can be on a shaft that rides on bearings, rather than
having bearings inside the idler.

This allows for a smaller diameter idler.
Attempt to improve responsiveness of 3d view
Correct paths to included files
Remove dead code
Prefix z axis things with z_