MVVM 아키텍쳐를 참고합니다
[https://medium.com/free-code-camp/app-architecture-mvvm-in-flutter-using-dart-streams-26f6bd6ae4b6]
참고 MVVM 데모 프로젝트
[https://github.com/shubham-chhimpa/flutter-mvvm-provider-demo]
ViewModel에 대한 설명 (KR) https://blog.yena.io/studynote/2019/03/16/Android-MVVM-AAC-1.html
UI, (View Model) , DataModel,
Screen(UI) --> ViewModel --> Service --> Service(API) --> DATABASE or STORAGE