Decide when the notification is handled

@MyMalcom 

After thinking a lot I though it would be better to do it this way. The app code is cleaner and more flexible.

This will let the app developer decide when the notification is handled. For example, he can redirect to another activity and handle the notification there.

We will use it in Decathlon and, since I think it is a nice feature to have, I decided to push it to the lib.

I updated the documentation, not only for this new feature but also for custom parameters.

(I admit that I am not completely satisfied with this solution. I would like to give the app developer more control over the notification creation, but this would involve a complex refactor).