revise the way that clear and shuffle work

 * protocol: ability to move items in multiple playlists at once
 * protocol: clear and shuffle commands removed
 * client: clear and shuffle buttons removed from UI
 * client: Ctrl+A to select all, works on queue, library, and playlists
 * client: shuffle works on the selection instead of the entire queue
   and also works on playlists and playlist items
 * client: shuffle context menu added to playlists and queue