Adjustable-tolerance LEGO-compatible brick customizer

Adds adjustable tolerance to cfinke's customizable brick so that you can experiment to get a good fit with LEGO bricks. On my Ultimaker 2+ with PLA, the following tolerances give the best fit:

Studs: -0.2 (Yes, you can use negative numbers to make the fit tighter.)
Walls: 0.2
Posts: 0.1