KP Republic BM16A case

I did a mico-level clean-up of the model's geometry. There are no substantive changes to the design but it is more-ready for your own remixes.

The part printed an exact-fit for the BM16a with plate. It has no give or rattle on three axis, but the PCB+plate can be removed easily. OP zackinzanebyrd's measurements were perfection.