Initial work on dynamic subsystem creation.

Initial work on dynamic subsystem creation.

Make subsystems create-able and removable from commands. Only some subsystems are supported so far, since many have non-default constructors or other complexities.

With this, change, it's possible to dynamically add and remove the traffic-manager at runtime, for example: fgcommand("add-subsystem", props.Node.new({ "subsystem": "traffic-manager", "name":"traffic-manager", "do-bind-init":1}));