Draft: Minimal a version of the stand with a Pi, no Sangaboard

From a tread on the Forum, the v6 is still liked because it is smaller overall when used without motors https://openflexure.discourse.group/t/help-with-translating-the-server-and-a-mass-distribution-project/1962/3.

The Manual version of v7 makes the body smaller. The standard v7 base with a Pi is larger than the v6 base, and uses more filament and time.

This MR creates a short base without the electronics drawer, to fit a Pi but no sangaboard. The walls are thinned to use less time and filament. The walls are more flexible, but this is stiffened when the microscope is screwed onto the top.

On Prusa Slicer this is ~59g, compared to ~40g for the v6 stand, or ~140g for the v7 stand and electronics drawer. It has a larger base area so is more stable than the v6 stand.