Working gradient descent for networks with 1xN junctions + an Example

The DTASolver launches the resolution of a simple network with both
a gradient descent computed by finite differences and by the adjoint method.

- Added a debug gradient descent by finite difference method
- Added SOPC_Optimizer.hava that computes the gradient by directly solving the
  equations of the adjoint
- A jUnit test checking the two methods give the same results
Added the execution times for the two methods.

The adjoint is slower than the finite differences for this small network.