Pop-up hook 80%

This is the [pop-up monkey hook](https://www.thingiverse.com/thing:4546353) by [clide](https://www.thingiverse.com/clide/designs), scaled down to 80%, which lets it print somewhat faster. Since the tolerances all shrank it was necessary to remodel the lid. There are a few other changes here:

* The mounting hole no longer has any kind of clearance inside the body. There's a new "hole mount plug" part that seats into the hole but is flush with the inner back wall. You can glue or weld it into place from the outside to make it permanent.
* There's a hole in the bottom of the lid that corresponds to a nub in the head model (and the blank model). This helps position the head consistently within the lid. The head should be printed upside-down. I haven't added this to the monkey head, but it is present on the eyeball model.

The eyeball model is from [Eyeball Father in a teacup](https://www.thingiverse.com/thing:4770751) by [reddadsteve](https://www.thingiverse.com/reddadsteve/de