mandos-ctl: Refactor: Move command list generation into argparse

* mandos-ctl (add_command_line_options): Don't simply set flags for
                                         each option; instead, add
                                         command objects to a
                                         "commands" list.
  (check_option_syntax): Rework to deal with an already-generated
                         command list.
  (commands_from_options): Remove all code to generate command list,
                           but add more code to move command.Deny
                           ahead of command.Remove in command list.
  (command.PropertySetterValue.argparse): New; used in
                                          add_command_line_options.
  (Test_check_option_syntax): Refactor to pass actual string arguments
                              to parse_args() instead of modifying an
                              argparse.Namespace.