Refactor StatusBar and changeNavigationBarColor calls

[SyntaxBlitz]

These functions get called all over the place, whenever a new screen loads, and it's not DRY.

We can:

• extract these calls into their own function to keep them DRY
• OR make this the responsibility of a listener on the navigator

[schonfeld]

This one is impl'd in #27 using a useStatusBarStyle hook