Create a Role to implement an Observable Design Pattern for Model

[marcoarthur]

Motivation

Model holds data retrieved. This data is wrapped on Objects. There a number of options to orderly increment
new functionalities based on these data pieces encapsulated into object as an attribute. To manage automatic
(dynamic) role application we can construct the observable pattern to Model and define Events for Model life-cycle such as creation, attribute change, destruction, serialization, and so on.

[marcoarthur]

We actually need just two events: the attributte setup and the model populated. That is when we create a model we will setup the values given, so we can attach any callback to attribute being set. When model is populated with a hash of its attributes we can just emit the event that represents this process. That are the basic thing that a model has to do in our app.