Fix block notify race condition

[victor-tucci]

• Replaces the hook system with std::function callbacks.
• Converts the block-added and verify-miner-tx hooks to throw an exceptions on error, rather than returning a bool.
• Rename the block-added to block-add because this hook is not for after the block add. it's for adding the blocks
• Add proper post-block-add hooks, and make them get used where suitable.
• Rewrite the trash tools::Notify code, and make it use a block-post-added hook rather than forcing its filth into blockchain.h.

Removed --block-rate-notify entirely; it's nearly useless on Beldex.

block and reorg notify remain, but now use a post-block hook rather than shoving toxic Notify crap into cryptonote_core headers.