[ Manuel de la Pena ] * Ensure that when there is a network error the state of the GroupDownload is correctly set. (LP: #1227850, #1227907, #1218031) * Provide system dbus API to be used by apps such as the image updates. (LP: #1211486) * Provide new arg and new method to simplify tests. (LP: #1228233) * Ensure that all downloads are canceled and that the files are correctly removed. (LP: #1229413)