I can't help you with making a playlist, also I had a look around for any scripts that might help but couldn't come across any. However, if all you want to do is make sure that all the songs in your Library are unchecked then you can use a keyboard shortcut. To check or uncheck all the songs in a list "Control and click" the checkbox next to a song. You'll need to do it twice, the first time will uncheck everything, the second will check everything. Hope this is of some use, if not I'm sure someone else will be along who can help with a way to identify your tracks.