Improved Einsy enclosure with removable door

There are a wide variety of remixes and custom Einsy cases (including my own) available… so why do we need another? I've looked in detail at a few different designs, and learned from my mistakes:

1. Having an enclosure that opens outward may seem convenient at first, but becomes unusable once you have an enclosure.
2. Many case designs result in motor wires having to cross over the Einsy board. This results in a mess.
3. Large cases take a long time to print and use excessive material; without significantly improving the wiring.
4. Unnecessarily restrictive licensing such as CC BY-NC-ND.

These considerations led me back to the stock Prusa Einsy box, but it has a number of shortcomings:

1. The cover gets in the way as soon as you open it.
2. There are several holes where the wall gets too thin.
3. The captive square nuts are a nuisance.

This design is a revision of the original OpenSCAD source code that significantly cleans up Prusa's design. It has a number of improvements:

1. Revised lid design that can be easily removed
2. Option to use heatset inserts instead of captive square nuts
3. Option to use self-tapping screws instead of hex nuts to mount the board
4. Made the case thickness more uniform to avoid holes and thin wall artifacts
5. Cleaned up code to make future modifications easier

The cable clips and hinges are identical to stock, and the lid is backwards-compatible. If you only want to replace the lid, all you need is a second small hinge (provided as an STL here for convenience).