Revert "applets/taskmanager: New grouped task style for themes without the normal graphic for it"
This reverts commit a0637a7c
The new style doesn't work as well as the old style for some types of app icons. Examples:
I think it will be hard to make stacking icons look consistently good and legible, so I don't see a way forward for that style. In !745 (merged), some users reported finding it harder to read. In my opinion, even though the older style wasn't perfect, it was more generally compatible with different styles of app icon.
We can use this MR as an opportunity for additional discussion if necessary.