Stackable Screw Box (divisions and robust)

Deixei mais robustos o fundo e a aleta de encaixe e criei divisões (2, 3 e 4 espaços).
Melhorias realizadas no projeto [Stackable Screw Box](https://www.thingiverse.com/thing:312717) (caixa de parafuso empilhável) de [Wick3d](https://www.thingiverse.com/wick3d).

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I made the bottom and the fitting flap more robust and created divisions (2, 3 and 4 spaces).
Improvements made to the project [Stackable Screw Box](https://www.thingiverse.com/thing:312717) by [Wick3d](https://www.thingiverse.com/wick3d).