Improved InstantSend fee estimation, ProTx JSON format fixes
Fixes:
- ProTx payload JSON formats - fix endianness of hashes, make correct service string, other JSON format improvements;
- When constructing special transaction from JSON,
extraPayload
field is now considered a hex string instead of JSON, per Dashcore's RPC docs; - Added
.estimateInstantSendFee
to theTransaction
class; Fixed fee validation for InstantSend transactions