user defined Jacobian for CVODE doesn't work

[logicabrity]

At the moment, we tell CVODE to estimate the Jacobian. We know that providing our own computation makes time integration work more efficiently.

As example fidimag/examples/micromagnetic/nmag_example_2_box/sim.py (not a test yet because it fails) shows, the computation hangs somewhere.

Need to fix this.

[davidcortesortuno]

This problem is running now with the new Sundials upgrade, but the diagonal and Jacobian precond methods, run super slow