Fetch the remembered group selection name. The returned value
may or may not actually be present in the list of tab names for
a given node.
If no value is stored for this node, will return the last selected
group name for a node that does have groups, such that if a given
tab is selected and the selected node changes to another node which
is unknown but has the same list of tab names, the selected tab
will not suddenly change.
If the name is not found, the caller should use PropUtils.basicPropsTabName()
as the third fallback for selection, setting the selection thus to the
Properties tab.