smartplaylists: add support for sort attributes (especially "ignorefolders")
smartplaylists: implement virtual folders inside smartplaylists
CGUIDialogSmartPlaylistRule: integrate virtual folders
smartplaylists: "playlist" is a browsable field
smartplaylists: add IsMusicType() and IsVideoType() utility methods
smartplaylists: add CheckTypeCompatibility() utility method
CGUIDialogSmartPlaylistRule: only show smartplaylists that match in type and are not grouped
Merge pull request #2988 from Montellese/xsp_extensions

smartplaylists: support for virtual folders