v0.37.0: Import from URL takes Spotify links

A Spotify track, album or playlist is read off Spotify's public embed
page, each song found on YouTube by the result closest to Spotify's
length, downloaded with the song flags, tagged with Spotify's
artist/title/album/track number, then imported and identified.

tests/test_round49.py

@@ -337,6 +337,8 @@ class TestWindow:
                 assert "T2" in description
             def chosen_entries(self):
                 return []
+            def spotify_tracks(self):
+                return []
             def download_urls(self):
                 return [self.url()]
             def exec(self):