Navigation-InitialPhase.swift

// taken from release/0.2

internal class OnboardingViewController: UIViewController {
 
	...
	private func pushRegistrationPage() {
		let registerViewController = RegisterViewController()
		navigationController?.pushViewController(registerViewController, animated: true)
	}
	
	private func pushLoginPage() {
		let loginViewController = LoginViewController()
		navigationController?.pushViewController(loginViewController, animated: true)
	}
	...

}

class LoginViewController: UIViewController {
	
	...
	@IBAction func signUpButtonTapped(sender: UIButton) {
		let viewController = RegisterViewController()
		self.navigationController?.pushViewController(viewController, animated: true)
	}
	
	func backToPreviousScreen() {
		self.navigationController?.popViewControllerAnimated(true)
	}
	...
	
}

internal class RegisterViewController: UIViewController {
	
	...
	@IBAction func pushLoginPage(sender: AnyObject) {
		let viewController = LoginViewController()
		self.navigationController?.pushViewController(viewController, animated: true)
	}
	...

}