Playing around with TestForwardPropagate.

[New] TestForwardPropagate added.
[New] proben1.example: example1.dt just for testing purposes.
[Fix] NeuralNetwork.loadTrainingSample(...) now operates with
      Input Data nodes, excluding Bias nodes. As it should be.
[Fix] InputNode: methods added to distinguish between Input Data
      nodes and Bias nodes.
[Fix] Sigmoid: bad parenthesis grouping solved.