add command parameter for Galaxy parser

Due to this line https://github.com/hexylena/argparse2tool/blob/cca59571ad18f0bcc7b863ebbdd42a3480801aaf/argparse/__init__.py#L144 this allows to get the xml only for a subcommand. No idea if this was intended like this? For consistency this could be added to the cwl part as well.

Author: bernt-matthias

argparse2tool/cmdline2gxml/__init__.py

@@ -23,4 +23,5 @@ def __init__(self):
 
     def process_arguments(self):
         self.parser.add_argument('--generate_galaxy_xml', action='store_true')
+        self.parser.add_argument('--command', action='store', default="")
         return vars(self.parser.parse_args())