Added PerExpansionNNPerformanceChangeStoppingCondition.

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

Changed dynamicPSOCascadeNN.xml to incorporate the new stopping
condition.
Merge pull request #144 from censlin/cnExpansionStoppingCondition

Added PerExpansionNNPerformanceChangeStoppingCondition.