Move GamdlError to utils and update imports

gamdl/downloader/exceptions.py

@@ -1,5 +1,4 @@
-class GamdlError(Exception):
-    pass
+from gamdl.utils import GamdlError
 
 
 class MediaFileExists(GamdlError):

gamdl/utils.py

@@ -95,3 +95,7 @@ class CustomStringFormatter(string.Formatter):
                 return fallback_value
 
         return super().format_field(value, format_spec)
+
+
+class GamdlError(Exception):
+    pass