Add a new default 'auto' argument to the 'kcdf' parameter in the GSVA method

[rcastelo]

Enable the GSVA algorithm to work with a new default value for the kcdf parameter, concretely a auto value, which will make the GSVA algorithm to decide automatically which approach to use to estimate the ECDF per gene, kernel based (Gaussian for continuous data and Poisson for discrete integer data) or directly without kernel (current value none).