Ignore gnome-doc-utils.make

Autogenerated file.
Better form for GtkApplicationwindow.py.page exercises

Some brackets eliminated, exercises written in a clearer language.
Alternative sample code for image modified.

An useless comment on the first alternative sample code for image
has been removed.
The application_id in the second alternative sample code for image
has been changed to org.gnome.ImageExample3 to conform to what
was done in the first alternative code.
Another change to the alternative sample code for image.

Another useless comment deleted.
gtk-beginners page for Python partially rewritten.

The language is more clear; the "how to run the code samples"
reflects how in the new format of the pages the code sample is not
the first thing you see; the reader is invited to modify and
"play" with the code samples provided in the synopsis.