Bear upgrade Rambo Mini Base upper/lower mount

This is just a quick remix of the upper/lower mount parts for the Prusa Bear upgrade (see Remix Info).
The original Parts are totally fine. I just did not like that a M3 thread should just be in a plastik part. Thats a no no for me. ;-)
Therefore i made it a slight bit beefier and added the cutout for the M3 Nut.
Of course did some chamfering and rounded the edges.