ecore: add an helper class Efl.Model_View

ecore: add an helper class Efl.Model_View

With the advancement of our MVVM interfaces, we realize that it could be made easier,
especially for bindings, to write an Efl.Model that proxy another one without having to
necessarily implement the entire logic of propagating event and checking if the property
we are getting request for is actually handle by our own Efl.Model. To simplify this,
I introduce this class that allow to set new callback for each property you want to handle
on your object.

Reviewed-by: Xavi Artigas <xavierartigas@yahoo.es>
Differential Revision: https://phab.enlightenment.org/D7487