Merge: Intro AppComponent to notify all elements of an app of its life cycle

The names of callbacks on the life cycle have been inspired by Android's. There is an equivalent to each of them in iOS, their naming is more precise but more complicated, so they looked less nity.

As of now, only `App` specialize `AppComponent`, but more users in the UI module will soon be introduced.

The implementation of this life cycle in mnit and the old Android implementation using the NDK is a bit awkward. But you will notice that it is much better in the newer NitActivity based implementation, which is the future!

Pull-Request: #1343
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Ait younes Mehdi Adel <overpex@gmail.com>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>