Added listsinceblock and modified WalletTxToJSON



 The command is needed to detect the newblock in an easy way.

As a reference. this is the snippet of ruby code that detects new blocks in our pool.
 

begin
                                aTransactions = coinClient.listsinceblock lastHash
                        rescue
                                shell.error "  * Error conecting with #{coin.symbol} daemon!"
                        end

                        if aTransactions.nil? or aTransactions['transactions'].nil?
                                shell.say "  > No new transactions"
                        else
                                aTransactions['transactions'].each do |transaction|
                                        if transaction['category'] == 'generate' or transaction['category'] == 'immature'
                                                newBlock = coinClient.getblock transaction['blockhash']
                                               
                                                oldBlock = coin.blocks.first(:hash => transaction['blockhash'])
                                                if oldBlock
                                                        oldBlock.confirms = transaction['confirmations']
                                                        if (transaction['confirmations'] > confRequired)
                                                                oldBlock.confirmed = true
                                                        end
                                                        if oldBlock.save
                                                                shell.say "  - Updated block #{oldBlock.hash[1..10]}... "\
                                                                        "#{transaction['confirmations']} "\
                                                                        "confirms (#{oldBlock.confirmed})"
                                                        else
                                                                shell.say "  * ERROR updating block!"