Starring shouldn't result in entire source list update

[sssoleileraaa]

Description

We currently update the entire source list in the GUI whenever a source is starred or unstarred. This is unnecessary since the star button is already toggled in the GUI.

Also, if the star job is unsuccessfully received by the server, is_starred will be updated to match what we have on the server on the next sync, which also updates the source list.

    def on_update(self, result):
        """
        The result is a uuid for the source and boolean flag for the new state
        of the star.
        """
        enabled = result[1]
        self.source.is_starred = enabled
        self.controller.update_sources()
        self.setChecked(enabled)