samples function has different declaration in Poisson with respect to Likelihood class

[adhaka]

The samples function which is called several times, especially when plotting, true predictive values with the option "m.plot_mean(...,plot_raw=False)" , there is an ugly error because of difference between the declarations of samples function in Likelihood class and corresponding child classes.

[adhaka]

quick fix would be to add the argument:samples=1 in the declaration.