Saddles Squared

Updated the model used for the horse saddles. The new version is completely pixel consistent.

Tweaked the saddle textures to match with their new models.

Made major changes to the skeleton horse saddle: Clipping has been eliminated, the saddle is now flush to the horse's spine, and the underneath is fully textured.

The skeleton horse saddle is now based off of the pre-1.14 textures used by skeleton horses.

Added built-in support for Undead Horse Variants.