Add a message page

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• 메시지 남길 수 있도록 기능 추가

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• firebase : read document by id

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• javascript string 공백 제거

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• [firebase : timestamp.now()](https://firebase.google.com/docs/reference/android/com/google/firebase/Timestamp#now())

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• 정규식 숫자만 허용 : /^[0-9+]*$/

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• firebase pagination