Add linearize method for blackbox systems

[ueliwechsler]

I could be a useful feature to have a linearize method for black-box systems which does compute the linearization at a certain point (x,u,w) for an arbitrary function f(x,u,w).

Using the fields statedim, inputdim and possibly noisedim.

To avoid any precompilation overhead, we should use Requires to load the used AD library.

[mforets]

I agree to add a linearization routine, ideally through existing tools as you propose. I have previously written some code that was using TaylorSeries for the computations, but i would have to clean it up.