Added customizable chunk generation rates
The rates define how many chunks are allowed to be generated in one tick per world, depending on the world type. This ratio is reevaluated everytime over time intervals of up to 5 seconds, before a chunk is generated by player movement. The tick timer which monitors the tick duration may prevent the generation of chunks, when there is much load, even when the defined rate has not been reached yet
If the PacketBuilderThreadPool has not been initialized yet, there is nothing to shut down