Auto-refresh feature

[jeffchao98]

Tech Plans

• Modified the LiveData in the ViewModel, which we need a in-model method for trigger the call-api-logic
  • For now, the logic inside is one-time logic when the observer been setup in the fragment
  • Can reference the article for learn how to do it
  • In the official document , we can find out how to use MutableLiveData().switchMap instead of Transformations.switchMap in the last reference article
• Implement the logic which can execute the logic repeatedly
  • Can reference this article for learn how to use Handler , Runnable
  • Place the countdown object and the related logic in Fragment, and execute the in-ViewModel method for call api and refresh the data
• Time period: 30-minute