Fix getArmorTexture by passing it the subtype

This fixes Item.getArmorTexture by getting rid of the useless layer argument (which could be mistaken for the render pass, but it's just 2 when the slot is the upper body armor slot, otherwise 1) and replacing it with the type argument that gets passed to RenderBiped.getArmorResource.

**edit:** Made some changes. The old getArmorTexture is now kept, but marked as deprecated.