major refactoring

- move instances to new file
- import functions as modules
- add docstrings to helper functions
- add threaded populate() function
- remove unused functions and files
- add typing info to helper functions
- other unremembered changes to the client

server/app/instances.py

@@ -0,0 +1,5 @@
+from app.models import AllSongs
+from app.models import Artists
+
+songs_instance = AllSongs()
+artist_instance = Artists()