Dip 158 remove ready for settlement

[YinonFirstDAG]

• Removed ReadyForSettlement command
• Added expectation for the Merchant VASP to find transaction on the blockchain
• Added abort codes for the AbortPayment command
• Added abort sequences (Missing Recipient Signature, Could Not Put Transaction On-Chain)
• Added appendix about including the reference ID in the transaction metadata (including reference to DIP-10)
• Removed sequence diagram temporarily (until we upload the final image to github and embed from there)