Fix Python warnings
After running the unit tests the logs in ~/gst-validate/logs/ptv_testsuite
can be grepped for "Warning".
There seem to be lots like this:
/home/aleb/dev/pitivi/pitivi/pitivi/viewer/guidelines.py:92: PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "label" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations
label = Gtk.Label(_("Composition Guidelines"))
Next, we can run the tests with PYTHONWARNINGS=error::DeprecationWarning
to convert the Python deprecation warnings to errors and see what makes sense to fix.
One warning type per commit, so it's easy to review!