Decontaminator-style Brush Holder with Sheet Stops for Blobifier

I don't recall if I changed any other geometry, but this works with my LDO-spec 300mm bed perfectly.  (Actual bed dimension is 305mm).  YMMV.

I intend to remove the decontaminator eventually and switch to its single pin sheet stop, but for now, I still have some clean operations in my PRINT_START happening over there.

Offset to the side for use with the Blobifier.