Add an IGNORE option to BlockResponse

[devos50]

Currently, there are three options on how to handle an incoming block: confirm, reject, and delay. The confirm and reject responses each create a new block, and the delay option adds the incoming block to the counter_signing_block_queue again. When creating a very basic community, I'm looking for an option to simply ignore incoming blocks. Therefore, I'm suggesting an ignore option, where nothing is done with the incoming block.