3.2 - Handle Dropped Packets

If a PoWClient receives a block that points to a block which has not been received yet (is not included in this.allBlocks), then the client fails. One simple way to handle is to just reject that block. The realistic way to handle this is to request the missing block(s) from peers. The realistic solution increases complexity fairly drastically as the implementation will involve use of asynchronous functions (e.g. async, await).