Implement Signing Service

[coder11]

Signing service is a built-it service, implemented in TS which allows to

• sign byte data using peer's SK
• verifying signatures using signed data and peer's peerID

[coder11]

Limitations of the first iteration:

• Supports only ed25519 keys
• Only supports single key = peer's keypair
• Hard-coded tetraplets

In future:

• Add support for multiple key pairs per peer
• Key is identified by it's public representation as peer id
• Configurable tetraplets (+ API)