This diff does two things:
1. Makes `RegistrationContainer` scrollable, so if there isn't enough space in the viewport, the content can still be fully viewable
2. Add `KeyboardAvoidingView` to the `RegistrationNavigator`, following the approach in `Profile`. This way when a `TextInput` is focused and the keyboard comes up, the `ScrollView` automatically adjusts so that the `TextInput` is still visible on screen
Depends on D7592