0.9.18: Bugfix for GUI, warning when copy_all_playlists cannot be used

#30 fixed, the issue was a GUI problem withe loading the playlists.

There seems to be a bug in ytmusicapi that has impacted one users ability to copy_all_playlists. I've filed a bug with ytmusicapi, and I've added some explanatory text. Unfortunately, the issue right now means that playlists will need to be manually copied.