incoming edge on stimulated nodes

[gabora]

incoming edge on input nodes do not lead to any problem.
checked with inputs:
- input_on_stim.sif (from ToyModelPB.sif, added gsk3 -| egf)
- ToyModelPB.csv
also tried with activation edge, egfr -> egf, gsk3 -> egf. all look fine.

I think user's should be notified that these edges make no sense in the simulation.

desired behaviour:
user get notified that incoming edge on stimulated nodes are not considered in the simulation. Run the optimisation since
this does not make a problem.

input_on_stimulus.zip