Under desk cable holders

This is a remix of dsw73's cable holder, with the main goals being offering more cable attachments on a single holder, and closing the holes on the back, where my zip ties were frequently catching. It did not totally resolve the catching problem, but it is distinctly better. The “slimmed” versions are a little thinner and lighter to cut down on the plastic needed, and also hold the cables slightly closer together. I haven't worked out whether I prefer that way or not. Edit: The “velcro strap” version uses a 12.5 mm wide velcro strap. It requires more bridging than the zip tie versions. I found that multiple holders in a row were hard to manage with the velcro, so I made a single holder of variable width. There's no provision to deal with the tag end of the strap. Making the groove underneath wide enough to allow wrapping the strap around multiple times worked, but makes the holder bulky, and made changing the cables slow, so I compromised on looks instead. The included OpenSCAD file should be easily customizable. If you don't have openscad handy, and want STLs made with any particular dimensions, please let me know.