Customizable Parts Drawer

Inspired by the work of AndrewBougie, I thought I'd have a go at creating a parametric version of a stylistically similar set of drawers, and learn how to use OpenSCAD at the same time.

## Parameters
### Basics Tab
These parameters are all in mm:

1. Unit Depth: How deep the drawers are.
1. Unit Width: How wide a single width drawer is.
1. Unit Height: How tall a single height drawer is.
1. Handle Thickness: The width of the handles.
1. Handle Depth: How far the handles project from t