MMU2 minimum color purge calibration tool

**Update 9/2/19**: I added a taller version that is easier to read but requires a bit more set up the first time. I added a .3mf to get you started. This prints at 0.5 layer using a 0.4 nozzle. It works. I definitely recommend this version. See below for how to use. I added a 5 color gcode for easy option.

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This calibration tool captures every permutation of color transition from 2 to 5 filaments in a single object. Print this to determine how much bleed is occurring beyond minimu