Added StoppingConditionDetectionStrategy.

This detection strategy fires when a stopping condition evaluates as true.
Added a Wilcoxon signed-rank test based stopping condition.

It statistically compares the performance of two NNs.
The code is adapted from the implementation in R-2.10.1
Some pre-merge editing.

Fixed the header in NNPerformanceChangeStoppingCondition.

Made static functions public and removed unneeded annotations in
OneTailedWilcoxonNNPerformanceComparator.
Added getClone to NNPerformanceStoppingCondition
Merge pull request #134 from censlin/nnPerformanceStoppingCondition

Added a Wilcoxon signed-rank test based stopping condition.