Modular Paint Stack core components

This is the core of the Modular Paint Stack (MPS), a customizable system for organizing paint tubes, paint bottles, brushes, and more. All pieces are customizable, but this includes the most common parts to simplify printing. The MPS consists of a few pieces. The front, sides, shelves, and back. The shelves are designed so that the inner portion (the part not supporting the brackets) is based on the standard 42mm Gridfinity units. The system supports shelves from 1 to infinity units wide, but these prebuilt models are available in 3, 4, and 5 unit widths, which should be the most common. This also includes Gridfinity shelves, so you can add bins and other custom parts. Fronts, sides, and backs print with a brimm to ensure they don't tip over. Gridfinity skeleton shelves print with an inner brim. Without it, I found there was a 50/50 chance of it moving out of place. Gridfinity solid shelves have supports. These can be a pain to remove. I recommend flexing the piece slightly and then us