- Normalized Fallback constructor to be the same of Widget (or Container).

- Normalized Fallback constructor to be the same of Widget (or Container).
- Removed Fallback::Constructor prototype since now Fallback are constructed
  just like any regular Widget.
- Renamed Widget::Constructor and Widget::Destructor in modules to
  bife_widget_constructor and bife_widget_destructor.
- Added some more check to dynamic object creation in Parser.