Cubic Carts

Adds changes proposed in https://www.youtube.com/watch?v=klsGsPY-Q9k

• includes copper rail (redstone level sensitive, 1 level = 0.1 blocks/tick)
• removal of max speed gamerule
• made drag apply exponentially
• the values are configurable in config/cubiccarts.json on the server. the drag calculation uses EvalEx to be evaulated at runtime, the config has a file watcher and updates on filesave