Add StatusBar plugin; set non-overlay style and match app's color

The plugin's settings are both in config.xml and in the app's javascript,
as the dark text (styleDefault) can only be set in JS.
Add hook to manually copy splash screen images for iOS

The Cordova CLI apparently does not properly handle splash screen images
yet, contrary to what the docs say.

Therefore, we use a after_prepare hook script to manually copy over the
images.