Remove need for sample riser by adding nut traps to taller XY stage

Steps to do

• New module m3_nut_trap_with_shaft based on the nut trap in compact_nut_seat.scad
• Stage thickness increased by 10 mm
• Using m3_nut_trap_with_shaft to hold on illumination dovetail (no trylinders)
• Using m3_nut_trap_with_shaft on top of stage (no trylinders)
• New nut trap test object
• Print and test nut trap test
• Change the platform for the low cost microscope
• Slide riser for new high stage
• Fix optics modules to be based of sample_z again but to be unchanged
• Print and test modified stage
• Remove sample and slide riser from build script?
• Add just_nut_trap_test.scad to the build script

Code changes that will need review

• big_stage parameter removed as it said it was not longer used and had to be true
• new parameter leg_height is the height at the top of the leg
• leg_block_t is the thickness of the blocks at top and bottom of legs (was equal to sample_t)
• stage_t - now calculated from nominal_height sample_height and leg_block_t

nominal height was created as sample_z was used extensively though the code in places that
should not change if the riser is incorporated into the main body.