[501] update_icons() uses animate() and transforms to actually turn mobs

This removes the need for mob sprites to be pre-turned. Mobs that lie down do so with an animation rather than appearing on their side. You can lie down facing THE LEFT OH SHIT. Note: Simple_animals aren't affected, just carbon mobs.

The "lying down" icon_states for everything you could equip are all now unnecessary. They aren't removed yet though.

The dmi changes are to make xenos all face upward so when they turn, they're lying down rather than facing south and looking like they're doing a handstand. They're not terribly good in some situations. I expect WJohnson to have a fix for this eventually after yelling at me.

Comments aren't changed. The overlays_standing list is still around because overlays is not a normal list, and BYOND's normal list functions are worth the extra cost of keeping a spare list of images.

I got the comments on the earlier pr, I'll fix those stated issues posthaste. Also I'll get a screenshot sometime.