Make MoonCat image generation have a consistent scale

Motivation

The pixel-scale of MoonCat accessories are half the size of MoonCat body pixels, and if an image is request of just a MoonCat, the output is not scaled up to match. Hence requesting an array of MoonCats all with ?scale=3 will result in them not all being the same relative scale.

Requirements

Update the image-generation logic to have scale=1 be the natural base scale of MoonCat accessories. Add an option to submit a scale=0 to be half that size (MoonCat pixel size), which is only valid to request if the MoonCat is wearing no accessories.