Multilevels embedding for the MAB HGF

[LegrandNico]

We need to polish the MAB example a bit and add multilevel solutions:

• Use a different response function based on the derivative of the continuous node at the 2nd level to account for the increasing uncertainty for unobserved bandits.
• Add a multilevel example (as far as I can see, once sample parameters from response functions #170 is merged no major technical roadblocks are on the way).