Draft: Implemented a Python wrapper for the Zbar GTK widget.

Zbar offers a GTK widget, which used to have a Python wrapper.

However, it was for Python 2 only.

With Python 3, GTK 3, etc, there is a new infrastructure for GObject-based structures (e.g., all GTK widgets, including the Zbar one). So, once the widget is somehow created and returned to Python, gi does some magic for which it is automatically recognized and all its methods and properties become accessible.

The only exception is zbar_gtk_request_video_size, for which I have added a wrapper. I could not find how to register it as a custom method for the ZBarGtk objects, so it accepts one as a first argument.

See the attached example.py script for further information on the usage.

For further information, please see #18219 (closed).