simple pistol stand

a simple pistol stand for presentation (made for a Walther P99) but might fit several other brands and models. (for example a Walther P88-9 does not fit)

I reworked the fusion file due to some problems when quickly changing measurements to fit certain other pistol models

the measurements can now be easily changed in the FX/params tab which allows a faster change of the mag_stand size (width, depth, height).

i added a chamfer on the bottom to make it easyer to remove the part from the heatbed while preventing damages to the edges.

the stand size changed too.