Inverted skins have multiple broken animations

Inverted skins, also known as upside down skins, no longer use a special animations for a lot of situations, such as crouching, riding, swimming or gliding. This causes all sorts of visual issues when using these skins. The animation for the upside down legs also causes them to be swapped, which isn't as noticeable.

1. Equip any inverted skin (Example: Nathan and Erik from the 3rd birthday skin pack);
2. Crouch, swim, glide or ride any mob.