[UI] palette group need icons
musescore palette has many groups, and inside there are elements.
There is a problem that every time I want to add something, I always expand & fold various groups to see the inside elements icons to find the right group, rather than look at the group names. It will be easier when user can choose from some icons, not from texts.
If you need an example, I noticed that Guitar Pro has a palette too, and it also give each group an icon, so user don't need to expand the group to choose it.