Add statusBarStyle property

We shouldn’t use `barStyle` for the application status bar style (different typdefs, with different values).

See:
`UIBarStyle` in [UIKit Data Types Reference](http://developer.apple.com/library/ios/#documentation/uikit/reference/UIKitDataTypesReference/Reference/reference.html)
vs.
`UIStatusBarStyle` in [UIApplication Class Reference](http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html)