Added the CascadeHiddenNeuronCorrelationProblem and unit tests.

This new class serves as the a problem to be used in optimisation
during the correlation phase of the cascade-correlation algorithm.

Some classes needed a getClone method and copy-constructor.
Added CascadeOutputLayerTrainingProblem and unit tests.

This problem is used during the output training phase
of the cascade-correlation algorithm.
Small thing that I forgot to commit.
Added correlation phase of cascade-correlation algorithm.
Added output phase of the cascade-correlation algorithm.
Some cleaning and refactoring in CascadeCorrelationAlgorithm.