Big Thanks to Frank Reininghaus, who helped me a lot with these
changes! :)

* Fixed the "Network browser" and "timeline" issues, by using the
KDirLister's itemsAdded(KUrl,KFileItemList) signal -> Use the
given Url to define the parent-child relationship.

* Changed the name of the slot "slotNewItems" to "slotItemsAdded"
for consistency with the signal.

* Use a QHash<KFileItem, ItemData*> instead of a QSet<KFileItem> to
store the filtered data (needed to keep the O(1) lookup for filtered
KFileItems in slotItemsDeleted + needed to fix bug 311912 "After
erasing a filter, some thumbnails randomly disappear")

* Made the determination of the "expandedParentsCount" slightly
simpler - just adding 1 to the parent's level (Also needed to fix the
"Network browser" and "timeline" issues)

FIXED-IN: 4.11.0
REVIEW: 109180