Customizable revised Ultimate Box Maker

This is a heavily revised version of The Ultimate Box Maker, but still true to the original design. Development occurs at https://github.com/jbebel/Ultimate-Box-Maker. Aside from a thorough cleanup of the code for readability, the following features are now supported:

* Editable back panel in addition to front
* Calculate the box size from the PCB size and margin parameters
* Horizontal or vertical text alignment arguments
* Variable panel and tab thickness separate from the box
* Square corners (no filet or chamfer)
* Parameterize all dimensions, such that the box is infinitely scalable. Doubling every parameter will double the box in all dimensions.
* Vents go through the floor and are scaled to fit the size of the filet.
* For larger filets, scale interior filets to make exterior and interior filets concentric.
* Decorations are optional
* Box fixation tabs can individually be placed on the top or bottom shell
* EXPERIMENTAL: Screwless designs for fixation tabs and PCB