Group color legend

[manthey]

We should show the group color and line weight in a legend. Perhaps this would be something to display next to counts and/or next to the group selector. For annotations that have too many elements to show, this would need to be somewhere else.

[manthey]

This can also be next to the group name in the annotation (not element) list.

[manthey]

@cooperlab Apparently we made an issue for this a few months back.