Some warnings/notes about the covers.
Refactor to remove duplication

Unfortunately, it's lost in a large-scale line-ending correction.  Diffs
are still usable, but they need to ignore whitespace.

This is what I get for not committing more frequently.
Remove separate switch distraction for now

It will come back, but it's a distraction for now
Start refactor to use centered cubes

Also fixed incorrect part depth due to ignoring difference between wall
thickness and end thickness.
Make mounting holes reusable
Make code more readable
Migrate cavity to centered cube
Top/bottom material cuts based on center