Regularisation

Implementation of NN weight regularisation (weight decay and weight elimination) for both PSO and backpropagation. PSO requires nothing but a regularisation decorator that wraps the NNTrainingProblem for the weight decay to work, while backpropagation has to set the regularisation (penalty) term in the BPVisitor. The difference is due to the fact that backpropagation uses the derivative of the regularisation function, and PSO does not.