Improve errors handling

[lxkuz]

1. We can use Faraday middlewares, logger for instance

    Momoapi.configure do |config|
      #...
      config.faraday_block = Proc.new do |f|
        f.use Faraday::Response::Logger
      end
    end
  end

2. Error will store transaction reference to be able to re-check transaction status even after errored/timeouted Momo API response