refactor: change transaction layout and use RLP encoding for signing / hashing

[oXtxNt9U]

Summary

• use RLP encoding for transaction signing and hash calculation
  (based on Type 2 / EIP1559 transactions which is the standard on Ethereum nowadays, see here for reference)
• replace crypto-signature-schnorr with crypto-signature-ecdsa
• extend signature implementations and add a signRecoverable method for recovering a public key from signature
• removed vendorfield
• removed expiration
• removed signatures (multisig will eventually be reintroduced for legacy use cases)
• renamed some fields to match ethereum more closely (e.g. amount -> value, fee -> gasPrice)
• added senderAddress as a convenience to the tx data

TBD

• tx type registry is now obsolete and could be removed entirely
• consider getting rid of custom tx serializer in favour of RLP (see signature / hash code). we need at minimum some glue code for the JSON-RPC endpoint in order to process metamask signed transactions (i.e. RLP decode tx into internal tx representation)

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged