Mini / Mini+ First layer Test

A 25mm square single layer test print for checking your 1st layer calibration.

For minimum clean up there is no brim, and a small handle to pull the print off the bed without removing the sheet.

g-code for both PLA and PETG

Two versions of g-code are now included with preheat for the original MINI with the MINDA, and without preheat for the MINI+ with a SuperPINDA.

The g-code with preheat uses start code by dennisscholing https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/309