fd_viewControllerBasedNavigationBarAppearanceEnabled should be defaulted to NO and should be honored in the viewWillDisappear method

[joshuafeldman]

When using this library it will create various issues since it is swizzling all instances of UINavigationController. The default for controlling the navigation bar appearance, fd_viewControllerBasedNavigationBarAppearanceEnabled, should be NO so that it doesn't conflict with other implementations. The user should specify if they want to turn this feature on.

[joshuafeldman]

Pull request with fix #148