Android modifications

For Android support, we want to do the following things to our code base:

• Import the react-native-vector-icons library via Gradle
• Swap out the TabBarIOS component for an Android-based solution using the DrawerLayoutAndroid and ToolbarAndroid components to create a navigation bar that contains a drawer that slides out to toggle between the current and previous months' expenses
• Replace any NavigatorIOS instances with Navigator
• Remove ProgressViewIOS
• Remove the ExpandableCell components in AddExpensesModal and replace DatePickerIOS with DatePickerAndroid
• Add any Android-specific files to components that require them

Installing the vector icon library

You should not need to do anything extra to have the react-native-vector-icons library installed...