Sort and capitalise items in the knewstuff-dialog tool's sidebar

Prior to this, the list of knsrc file entries in the sidebar was just whatever sort order we got from Engine, and things without an explicit name set in the config file were just given the filename. This makes the list a little more more pleasant to read and navigate, by first transforming the filename to something more akin to a real string, and then sorting the list in a locale aware fashion.