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
Added PerExpansionNNPerformanceChangeStoppingCondition.

It similar to NNPerformanceChangeStoppingCondition, but is only
performed when an expansion in the NN architecture is detected.