elementary: add Efl.Ui.Widget_Factory.
The Widget_Factory is in charge of creating any object that inherit from Efl.Ui.Widget Class.
If the style property is connected to a model property, it will fetch it and build the widget
with that style. This factory is to be used with every View.
Reviewed-by: SangHyeon Jade Lee <firstname.lastname@example.org>
Differential Revision: https://phab.enlightenment.org/D7704