FlashForge Creator X and Pro gantries for S3D visualization

These are machine "printer models" for use by Simplify3D (S3D) V3.0 for workspace visualization. See the discussion at https://forum.simplify3d.com/viewtopic.php?f=8&t=2356 for options on how to instruct S3D to use these in place of its default printer-like object in the build space.