added superclass for download sources

src/music_kraken/audio_source/sources/source.py

@@ -0,0 +1,15 @@
+from typing import Tuple
+
+"""
+The class "Source" is the superclass every class for specific audio
+sources inherits from. This gives the advantage of a consistent
+calling of the functions do search for a song and to download it.
+"""
+
+
+class Source:
+    def __init__(self):
+        pass
+
+    def get_source(self, row) -> Tuple[str, str]:
+        return "", ""