Adds a dictionary to the prefs

def add_dict(self, dyn_dict):
        'Adds a dictionary to the prefs'
        if not isinstance(dyn_dict, dict):
            raise Exception('DynStruct.add_dict expects a dictionary.' +
                            'Recieved: ' + six.text_type(type(dyn_dict)))
        for (key, val) in six.iteritems(dyn_dict):
            self[key] = val