Fleshed out configuration and state reporting concept.

Introduced FlowNode which encapsulated the basic properties of
a node in the data flow. It has a position, name, id and the
possibility to retrieve and set such properties as well as update
its creator of changes.
Modify and extend FlowSupervisor to be closer to an interface.

Previously the Supervisor relied purely on ActorRef handles when
communicating to the outside. As the web-interface isn't actually
meant to interact with the actors in the background itself and the
browser won't have any notion of the meaning of an ActorRef it
now uses unique IDs instead.