feat: move storage path setting to configuration file

- change default storage path to /srv/libretime
- remove music dirs table
- use /tmp for testing storage
- storage dir should always have a trailing slash

api/libretime_api/settings/testing.py

@@ -1,8 +1,11 @@
 import os
 
+from .._fixtures import fixture_path
+
 os.environ.setdefault("LIBRETIME_DEBUG", "true")
 os.environ.setdefault("LIBRETIME_GENERAL_PUBLIC_URL", "http://localhost")
 os.environ.setdefault("LIBRETIME_GENERAL_API_KEY", "testing")
+os.environ.setdefault("LIBRETIME_STORAGE_PATH", str(fixture_path))
 
 # pylint: disable=wrong-import-position,unused-import
 from .prod import (