[Feature Request] Use included screenshot

[Drsheppard01]

I think the best UX is to use the screenshot specified in appdata.metainfo. I even wrote a small parser (I managed to get the right result, but I'm sure it won't always be like this)

cat $METAFILE | grep '<image type="source">' | sed "s/^\ *<[^>]*>//g;s/<\/[^>]*>//g" | cut -d'>' -f2  # For 1 screenshot
cat $METAFILE | grep '<image>' | sed "s/^\ *<[^>]*>//g;s/<\/[^>]*>//g" | cut -d '>' -f1 | head -n1 # For multiple screenshots

Benefits:

• User see app in better resolution
• this will simplify worker.sh

Warning:

Not all include appdata.xml or metainfo.xml in your AppImage