Properly display parent folders when filtering is active and items are added or refreshed
I have adapted the methods slotRefreshItems(), slotItemsAdded() and slotItemsDeleted() so they are now compatible with the new behavior of filtering expanded folders achieved in !271 (merged). Meanwhile I also fixed the bug where the parent expanded folder would disappear after adding or refreshing an item while filtering (this bug preexisted !271 (merged)).
This is one example test case that was bugged before and now is fixed:
There are countless more test cases that were bugged before and are now fixed.