"Notary" update👨‍⚖️👩‍⚖️

• Implemented offchain signatures #52
• Allow more than one signature in every POST
• Support Contract signatures
• Return 200 instead of 404 for empty lists
• Use 201 CREATED instead of 202 Accepted for POST txs
• Don't calculate unique nonce if no txs
• Run DB migrations on worker
• Optimize database indexes and SQL queries
• Use trace_block for last indexed blocks
• Add NFT transfers to incoming-transactions endpoint #76
• Call decode internal txs just if new traces are found
• Decode CPK creation data #78