Stackable shelves - parametric

Stackable shelves for when you get annoyed by the front of your bins and realize you wanted shelves all along.

Very similar to [my stackable bins](https://www.thingiverse.com/thing:5943586) but with no front.


**NOTE:** I updated all bins and shelves on 2023-10-31 (happy Halloween) to make any bin and shelf with the same width and depth compatible with each other for stacking. This does mean that all models printed before this change are incompatible with the new models.

I Included various common sizes as well as the Fusion 360 file if you want to choose your own—the f3d file is fully parametric.