modularize src

+ merge main.py and manage.py
+ move start logic to swingmusic/__main__.py
+ add a run.py on the project root

swingmusic/serializers/playlist.py

@@ -0,0 +1,13 @@
+from dataclasses import asdict
+from swingmusic.models.playlist import Playlist
+
+
+def serialize_for_card(playlist: Playlist, to_remove=set()):
+    p_dict = asdict(playlist)
+
+    props = {"trackhashes"}.union(to_remove)
+
+    for key in props:
+        p_dict.pop(key, None)
+
+    return p_dict