Replacing CoroutineScopes with viewModelScope

[Mrtckr008]

Based on #22

Problem

Using CoroutineScope instead of using viewModelScope inside viewModel.

Solution

The replacement has been made based on the following description;
Using a viewModelScope within a ViewModel is a more convenient, safer, and easier way to create and manage a CoroutineScope. viewModelScope automatically cancels processes and ensures that they are run on the correct thread, so it's the more preferred approach overall.

Test

Tested whole application features on Google Pixel 3.