Implement viewControllerWillUpdate and viewControllerDidUpdate in ViewController

[cipolleschi]

Issue
While working with tempura and VC, it happend several times that, when overriding the update(with state:) method we forgot to call super.update(with:)
Without that invocation, the view will not receive the new VM and the view's update(oldState:) method is not invoked.

Proposed solution
In the VC, change the update(with state:) in something like:

func update(with state: State) {
  viewControllerWillUpdate(with: state)
  // current update implementation
  viewControllerDidUpdate(with: state)
}

In the App's VC, the developer should override the methods vcWillUpdate(with: state) and vcDidUpdate(with: state) instead of the update(with state: State).

In this way is impossible to forget to pass the updated ViewModel to the View.

[smaramba]

done in version 0.6.0.
The ViewController has willUpdate() and didUpdate() methods.