Add automatic generation of Sdn Flow Routes

Suppose there is an SDN switch(S) and a server which hosts an SDN controller(C).
For every flow which is routed via S, an SdnFlowRule has to be modeled.
S now has to interact with C. Therefore we use SdnControlFlow instances.
We need an SdnControlFlow from S to C (called forwardFlow in the transformation) and an SdnControlFlow from C to S (called backwardFlow).
We assume that for every flow that is routed via S the corresponding SdnControlFlows can take the same route (i.e. the same Direction instances, except for their flow property).
To simplify modeling it is no longer required to model every SdnControlFlow and Direction instance.
We can now model the SdnControlFlows and Directions for one parent flow and automatically generate them for all other parent flows (in the context of S and C).
This is done in DNI3/etl/DNI-sdn-routing-DNI.etl, which is executed even before the routing transformation