modularize src

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

swingmusic/utils/generators.py

@@ -0,0 +1,9 @@
+import string
+import random
+
+
+def get_random_str(length=5):
+    """
+    Generates a random string of length `length`.
+    """
+    return "".join(random.choices(string.ascii_letters + string.digits, k=length))