Added support for a validation set in NNSlidingWindowTrainingProblem.
Added MSEValidationError measurement for neural networks training.
Added a NN measurement: the number of non-zero weights over the total number of weights, reported as a percentage.
Non-zero weights are defined as weights closer to zero than some epsilon (threshold).
This measurement may be used to report the percentage of irrelevant weights in NN training.
Hotfix: fixed error where the patterns were partitioned from the entire dataset, and not the current window 'candidateSet'.
Removed uid that was not unique from MSEValidationError class
Merge pull request #198 from sighmin/pull

NN Additions