Simplify getting known args

cura_app.py

@@ -16,8 +16,7 @@ parser.add_argument('--debug',
                     default = False,
                     help = "Turn on the debug mode by setting this option."
                     )
-known_args, unknown_args = parser.parse_known_args()
-known_args = vars(known_args)
+known_args = vars(parser.parse_known_args()[0])
 
 if not known_args["debug"]:
     def get_cura_dir_path():