Raspberry pi 3B+ case for 3030 beam - rear clips

Remix of the bottom case from https://www.prusaprinters.org/prints/40277-raspberry-pi-3b-case-for-3030-beam-octopi moving the clips to the rear of the case so the Pi can be installed lengthwise from the extrusion, similar to https://www.prusaprinters.org/prints/56428-prusa-mini-raspberry-pi-3-3030-mount.

This was done in TinkerCAD by simply cutting and moving the clips, so the result is a little shoddy (e.g. it blocks some of the power light opening), but it works just fine.