Changed ViewControllerLifecycle implementation using swizzling

[fabfelici]

Hello! This PR changes ViewControllerLifecycle implementation to a swizzling based approach because I noticed some issues with the existing child view controller approach:

• If you have a UINavigationController and you start observing the events on it, the rootViewController of the navigation controller will be swapped with a WrapperViewController resulting in an empty view. TabBarController is potentially open to same type of issue.
• If you are implementing a container view controller and need to also observe its lifecycle via reactive the children array could become hard to manage.
• Some crash detection libraries inspects the view hierarchy when a crash happens and if there is a view controller containing the WrapperViewController as child, the stack trace messages become hard to understand because of these WrapperViewController noise.

I don't like that this solution is based on swizzling but I believe there's no easy way to address this without creating a base UIViewController subclass that all the other VCs have to subclass.
This piece of code was also untested and I added some tests on top of it now, let me know if you see any issue!

cc @ibrahimkteish