Pass back the location of the downloaded files in queue items

This allows a third party user to locate downloaded files from a
previous session (i.e. if they weren't connected to receieve the
updateQueue requsts)

deemix/app/downloadjob.py

@@ -517,6 +517,7 @@ class DownloadJob:
 
             logger.info(f"[{track.mainArtist['name']} - {track.title}] Track download completed\n{writepath}")
             self.queueItem.downloaded += 1
+            self.queueItem.files.append(writepath)
             if self.interface:
                 self.interface.send("updateQueue", {'uuid': self.queueItem.uuid, 'downloaded': True, 'downloadPath': writepath})
             return result