Stringinging cubes test

These cubes are perfect to check stringinging (and multiple check for other tests).
There is a bottom layer connecting the cubes so you can mark and keep them.

I normally check with new filaments by default:
* slicing with 0.2mm, 2 perimeters, 1-3 bottom layers, no top layer and no infill.
* choose a reasonable speed (50mm/s) (modify later by GCode M220 S)
* "normal" temperatures for bed and hot end (modify during print to check for influence of temp)
* travel speed to 200mm/s
* retract