Documentation : Need to edit class_argonautActions.inc for custom modules

As discussed with Côme in an dev-session we need some easier way to add custom argonaut-actions to the drop-down in the systems-view.

Until now one has to edit class_argonautActions.inc for this.

In Addition it may be a nice-to-have if a custom parameter can be send along to the client (e.g. a shell-command to execute on the client).