Class CustomHeadTest

Adds a blaze head block and item to test the event for registering a custom skull model and to demonstrate the proper way to register a custom mob skull. To test it, locate "blaze_head", and test the item model, the model in the players head slot, the model in an armor stand, the wall block model, and the floor block model. Should appear identical in shape to vanilla heads such as zombies or skeletons, but use the blaze skin.