Prusa Filament Buffer Plate - Enhanced and Printable

# Statement
Prusa released their "Filament Buffer" with the MMU2S update but there was no STL for the plate on at [MMU2 GitHub](https://github.com/prusa3d/Original-Prusa-i3/tree/MMU2). There is a file named s-buffer-plate.dxf in the SCAD directory but the plate is too large to print with the MK3 and they had it manufactured, thus no STL.

The buffer is a necessary update but I found it quite difficult to push filament from the buffer to the MMU. I have several brittle filaments that were alm