Implement message signature logic

[appaquet]

This is needed to sign frames, blocks, messages, etc. Framing support signature, but it's only hashing the message using SHA3 256 right now.

Possible signature source:

• SECP251K1 to sign the 32b SHA3 256 hash. This will result in a 64b compact signature.

Problems:

• If we sign every since operations, blocks, messages, this may result in bloated chain and performance hit. Think about how we could have a hybrid. Blocks are important to sign, but messages a bit less.