Set the tintColor in the auth view and modal views navigation controller on iOS 7

- The authentication controller now sets the buttons tintColor always to the default blue color. This fixes white UIWindow tintColor, since the auth view is using white as background.
- Navigation controllers for modal views now also set the tintColor of the navigationBar to the default blue color on iOS 7, if the developer did not set the `navigationBarTintColor`. This fixes white UIWindow tintColor for feedback and beta update modal views as they are defined to use the default style.
testIntegration call should also send SDK name and version
Issue #85: Replace kNilOptions with 0

Thanks to Jonathan!
Add apps CFBundleVersion to the testIdentifier call
Make sure the authentication window is always correctly dismissed

If there would not be any rootViewController (which iOS now requires though), it could happen that the auth window would not disappear upon successful authentication. The app would have had to be killed and started again to proceed.
Show an alert if the authentication token could not be stored into the keychain

If this occurs, the user has to authenticate every time the app starts or even when the app comes into foreground, depending on the `restrictionEnforcementFrequency` setting