Get finite support

@lileicc @cberzan Here I add the methods getFiniteSupport() to each distribution. This will be used for implementing Gibbs Sampling.
perhaps this could work. The problem is knowing the size of the support apriori. For some of the getFiniteSupport distribution methods, we discard elements that have very low probability. For multinomial getFiniteSupport, I think you would have to run a Dynamic Program to find out the number of elements.