'Implement this method and :meth:`save_settings` in your plugin to
use a custom configuration dialog, rather then relying on the simple
string based default customization.
This method, if implemented, must return a QWidget. The widget can have
an optional method validate() that takes no arguments and is called
immediately after the user clicks OK. Changes are applied if and only
if the method returns True.
If for some reason you cannot perform the configuration at this time,
return a tuple of two strings (message, details), these will be
displayed as a warning dialog to the user and the process will be
aborted.'

def config_widget(self):

    raise NotImplementedError()
