[KFilePlacesModel] Improved closestItem algorithm

• Check query and fragment for closest parent: This ensures that baloosearch:?searchString=foo is considered the parent of baloosearch:/images and winning over it because it's longer
• Check for convertedUrl in closestItem: Matches setUrl behavior and ensures that for example baloosearch:/foo/bar is considered a descendant of search:/foo

@ahmadsamir @ngraham @meven

• "Search for: Documents" is now highlighted properly when browsing it
• KUrlNavigator is no longer confused when browsing "Search for: Documents" while having a custom search (Search → type something → "Add to place") in Places