Write default configuration on startup (bug 1511)

When no configuration file exists, write the defaults
to the configuration file, so users using the CLI have
an easier time modifying the default settings.

src/gpodder/config.py

@@ -132,6 +132,10 @@ def __init__(self, filename='gpodder.conf'):
 
         self.load()
 
+        # If there is no configuration file, we create one here (bug 1511)
+        if not os.path.exists(self.__filename):
+            self.save()
+
         atexit.register( self.__atexit)
 
     def __getattr__(self, name):