btcjson: map all bitcoind errors in one place

[yyforyongyu]

As of today, we have multiple places to match the errors returned from bitcoind RPC responses. We should instead build it inside btcjson for better maintainability. We can collect all the errors from,

• https://github.com/bitcoin/bitcoin/blob/master/test/functional/data/invalid_txs.py
• https://github.com/bitcoin/bitcoin/blob/master/test/functional/mempool_accept.py

and do a string pattern match and turn them into a new set of error types inside btcjson.