j4status-plugins: Adapt to upstream changes

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
hatari: libpng is now slotted

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
gthumb: libpng is now slotted

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>