Fix spoke drawing oddity

The rectangles weren't centered before rotation
Split shaft_diameter into inner and outer
Carve out the shaft's outer diameter from the legs

Legs need to go beside the shafts
Adjust fillets
Add spoke_z_offset (spokes are inset a little)
Fix shaft_outer_diameter
Update more dimensions

legs_diameter and body_top_diameter aren't right
Increase spoke_thickness

It was wrong.