the efl_canvas_group should be abstract in order to support other
abstract classes which are inheriting from it (efl_ui_widget).
This is done in order to support only abstract parents from abstract classes, which is needed for bindings, since most class systems are not permitting this.
The special problem here is that efl_canvas_group is instanciated in the pager and for legacy applications, for those two usecases a new class has to be established which simply inherits from Efl.Canvas.Group in order make the abstract class instancable.
Depends on D7599