Fix several sort-issues

- Treeview: When sorting descending assure that the parent item is still
ordered before the child items and not afterwards.
- Treeview: When sorting by other roles than names expansionsLevelCompare()
had been buggy and resulted in ordering child items below wrong parent
items.
- General: When sorting by another role than names and the role of
two items had been equal a case sensitive sorting of the names had
been done. This has been fixed by using the default name sorting
as fallback.


FIXED-IN: 4.8.0