MP Select Mini Z Spacer (snappable)

I remixed xilvar's customizable spacer for the MP Select Mini. The original had two versions. One with handles that could be inserted without disassembly, but left the little handles sticking there, and another without the handles that required disassembly.

This is my attempt to get the best of both worlds. When INSERTION_LEVERS is turned on now, it comes with little triangles notched out. Once inserted it should be easy to break off the handle/levers and take them out. You may require