modularize src

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

swingmusic/crons/cron.py

@@ -0,0 +1,23 @@
+import schedule
+
+
+from abc import ABC, abstractmethod
+
+
+class CronJob(ABC):
+    """
+    A cron job that will be run on a regular interval.
+    """
+
+    name: str
+    hours: int = 1
+
+    def __init__(self):
+        schedule.every(self.hours).hours.do(self.run)
+
+    @abstractmethod
+    def run(self):
+        """
+        The function that will be called by the cron job.
+        """
+        ...