Fixed Single/Double cooling fan with Effector hook mounts

I remixed this fan shroud because the original remixer didn't respond to a comment that he had a bug. If you print this for one fan, it retains little blocks that are required when you have two fans - to stop one fan from back-feeding into the other, but when it was remixed into a single fan shroud, the blocks were left in so that only half of the lower ring feeds.

I have also added two partially parametric hooks which are meant to let this device hang from an effector that does not have a w