graphics/py-img2pdf: Update to 0.4.4

• Add GUI option to reflect the requirements given in setup.py and to make use of the graphical frontend script.

• Simplify "do-test" target by switching to USE_PYTHON=pytest.

Changelog since 0.3.5 :

https://gitlab.mister-muffin.de/josch/img2pdf/src/tag/0.4.4/CHANGES.rst