Implement round-trip recognition

[simnalamburt]

Indicate that the transfer is completed when the message finishes the round-trip.

TODOs

• lines: List Line -> lines: Array Line → Not going to do it
• Remove LineStatus type from Line → Not going to do it
• 지금 새 메세지 들어올떄마다 list ++ [ new ] 이렇게 하고있는데 이거 new::list 로 고치기
• TransmissionStatus: Dict Int LineStatus 타입 생성
• Rename: ReceiveLine -> ReceivePayload
• ReceivePayload 에서 Session으로 비교하여 TransmissionStatus 업데이트하는 코드 넣기

[simnalamburt]

I'm working on it at mqtt branch.