Allows adding bones

Example: ```java // Context World world; // some world Location location; // some location Spider spider; // some spider // Create an ItemDisplay (spider.itemBones) or BlockDisplay (spider.blockBones) ItemDisplay display = world.createEntity(location, ItemDisplay.class); display.setTeleportDuration(1); display.setTransformation(new Transformation( new Vector3f(0, 0.5f, 0.5f), //x > 0 is left, y > 0 is up, z > 0 is front new AxisAngle4f(0, 0, 0, 0), // if you would like to rotate to the left new Vector3f(1.25f, 1.25f, 1.25f), // the size new AxisAngle4f(0, 0, 0, 0))); // if you would like to rotate to the right ItemStack skull = new ItemStack(Material.WITHER_SKELETON_SKULL); display.setItemStack(skull); display.setItemDisplayTransform(ItemDisplay.ItemDisplayTransform.FIXED); // Let the spider "connect the dots" spider.getItemBones().add(head); ``` Example in-game: