Added "Artwork by" in gettext, both to src/about.py and po/blanket.pot

[Porrumentzio]

Since now that wasn't translatable. Creating new po from pot with Poedit works well and adds that string, but I don't know how to update po files.

[Porrumentzio]

I achieved to update a current Basque po, but not all at once.

[rafaelmardojai]

This string is translated in the toolkit level. We don't need to translate this again.

[Porrumentzio]

So it should be translated on Gstreamer?

[rafaelmardojai]

GTK https://gitlab.gnome.org/GNOME/gtk/

[Porrumentzio]

Thanks, I'll update those translations.

[rafaelmardojai]

As a note, to update translations with potfiles changes, you should:

# Build
meson builddir
# Update
ninja -C builddir blanket-update-po