Customizable parametric LED strip diffuser

Parametric diffuser for LED strips.

Parameters (in milimeters) :

* `length` - length of LED strip you want to cover (in my case, 50mm per segment)
* `width` - width of the LED strip (usually around 10mm)
* `height` - height of the LED strip, with diodes (in my case - 2mm)
* `thickness` - thickness of the diffuser to be
* `spacing` - distance between LED strip and the diffuser
* `close_front` - should it have closing lid in the front (true/false)
* `close_back` - should it have closing lid in the back (true/false)