Upright z cable tidies

Add a cable tidy for the z-axis on the main body for the upright microscope.

This is part of #370

• Make cable tidies a scad library file
• Make sets of cable tidies for inverted and upright versions
• Add upright cable tidies to build script
• Use upright cable tidies in upright printed parts
• Render upright z cable tidy and screws in mount motors
• Update mount motor instructions to include cable tidy
• Put nuts in z motor lugs for upright as well as inverted (in renders and instructions of prepare main body)