Filament spool holder - clip-on base extension

Since the original base of the spool holder is rather small my printer managed several times to pull so hard on the filament that the whole holder tilted. To prevent this I designed a base extension that clips onto the original base.
Probably undersized the "hooks" a bit, they don't really snap, but there's still enough friction that it fits pretty well.
Also added 15mm indentions on the bottom for rubber feet.