Add more tests (and fix the score delete command)

Additionally, add a cli analogue of `score magic` (the `analyse`
subcommand)

migrations/04-auto-delete-scores/up.sql

@@ -0,0 +1,7 @@
+-- Automatically delete all associated scores
+-- every time a play is deleted.
+CREATE TRIGGER auto_delete_scores AFTER DELETE ON plays
+BEGIN
+  DELETE FROM scores
+  WHERE play_id = OLD.id;
+END;