Add distributions from stats package for presentation, fitting and random sampling

[rdstern]

This is not urgent, but useful when a programmer needs a new (small) task. A number of dialogues make use of the set of distributions. They are in particular the Model > Probability Distributions > Show Model and also Model > Probability Distributions > Random Samples and Model > One Variable > General

a) There are 4 distributions missing from the stats package and these could usefully be added and checked: This could be done together or any one added would be useful: a1) Beta distribution a2) Cauchy Distribution a3) Hypergeometric distribution a4) Multinomial distribution

b) The birthday distribution is useful. First check (script window by tweaking from another distribution) that it is useful for the show model dialogue. Then it is different, because it is not relevant for the random samples or the fit model dialogues.

c) Similarly check if arima.sim can be added (just called arima) This is to simulate from an arima process. It is for random samples, but not for the probability distributions or the fitting.

d) We already have chi-square and t distributions. But they each could have a non-centrality parameter. This should be easy to add. It applies generally to the show model, random sampling and fitting.

[N-thony]

@Vitalis95 do you still have some work to complete this issue or it is fully done?