smartplaylists: add support for sort attributes (especially "ignorefolders")
smartplaylists: implement virtual folders inside smartplaylists
CGUIDialogSmartPlaylistRule: integrate virtual folders
smartplaylist: "playlist" is a browsable field
smartplaylists: add <icon> support for custom icons/thumbs
WIP: CGUIDialogSmartPlaylistEditor: add control to choose an icon
WIP [confluence] add control to choose icon to SmartPlaylistEditor.xml