[Task Manager] Allow non-file "Recent Documents"
This allows recent documents to include folders (e.g. visited places in Dolphin) as well as other protocols, such as "vnc://foo" for recently connected remote desktops. Moreover, it adjusts the "Recent Files" heading to be more precise: * "Recent Downloads" when all files are in the Downloads folder, e.g. for a browser with plasma-browser-integration * "Recent Places" when all items are files, e.g. for a file manager * "Recent Connections" when all items are remote URLs without file name, e.g. remote desktop or server URLs