fischertechnik connecting block 7.5mm

I always felt the Fischertechnik [7,5mm building blocks](https://ft-datenbank.de/details.php?ArticleVariantId=85849bf0-b84b-4ee1-a636-9df31706a34e) could need a complementary building block that would allow to not only use them for additional distance, but also as building elements in their own right by enabling perpendicular constructions.

If you find that the pegs don't fit well with your ft factory parts, try to experiment with cura's horizontal expansion settings.

Please consider leavi