Enable navbar to have content drawn under it

[crutchcorn]

Ideally, we'd use a cross-platform React Native library to detect what the safe bottom distance is to add margins for:

https://github.com/th3rdwave/react-native-safe-area-context

It is unsure if this is the correct implementation. If it is not, we'll have to do a lot of that work ourselves:

https://developer.android.com/reference/androidx/core/view/ViewCompat#setOnApplyWindowInsetsListener(android.view.View,%20androidx.core.view.OnApplyWindowInsetsListener) https://chris.banes.dev/2019/04/12/insets-listeners-to-layouts/

Or even:

https://github.com/fennifith/Status/blob/master/app/src/main/java/com/james/status/utils/StaticUtils.java#L68 But with navigation_bar_height instead of status_bar_height

[crutchcorn]

Closing in favor of #9, as that's the last issue to resolve before merging into master