Proposals:Refactoring of optimization framework

Refactor Optimization Framework Based on Available Function Derivative Information

Modification to cost function hierarchy

Currently all cost functions are subclasses of itk::SingleValuedCostFunction or itk::MultipleValuedCostFunction. These two classes are pure virtual, forcing the user to implement a GetDerivative() method. This assumes that the optimized function is differentiable. When this is not the case, developers either provide a bogus derivative which is problematic if they unintentionally use an optimizer that utilizes this information or they can throw an exception.

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