Fork monitoring plugin

[theoreticalbts]

This plugin would save each incoming block in block_id.bin / block_id.json file, then delete the file when the block becomes irreversible. If the plugin's running while the network's forking, the blocks that end up on minority forks will never be deleted. Allowing us to preserve them to analyze why the network's forking.

[sneak]

That's a neat idea.

[mvandeberg]

For a first step, let's idump the blocks so that we can catch them in our logs, rather than saving them and trying to get them off our nodes.