Make it possible to configure sub elements for nodes (param, sender, listener).

[philipsens]

Is your feature request related to a problem? Please describe. The Frank!Flow can't perform all tasks.

Describe the solution you'd like Implement adding subelements like "params", "senders" and "listeners". These should have their own attributes, like nodes.

[diedekerkhof]

Implement basic subelements to Node, for now do this hardcoded.