EasiYo Yoghurt maker replacement lid outer

My EasiYo yoghurt maker lid fractured due to heat and UV damage, so instead of going to a shop to buy a replacement (now in multiple colours!), "I make a new one".

This is a simple OpenSCAD `hull()` design which fits nicely on the original red inner part of the lid replacing the outer shell. There is a polystyrene disc insulating disc sandwiched in the middle, which was a bit snug so v2.0 has an extra 5mm of height.

The outer curves are gentle to allow printing without supports.