nondeterministic feature selection

[ppdebreuck]

The feature selection procedure relies on mutual_info_regression & mutual_info_classifwhich is stochastic. Therefore, feature selection is nondeterministic (the ranked list of optimal descriptors can have slight changes from run to run).

Solution:

• Fix random state in mutual_info_regression See here.
• Average over multiple runs

Issue reported by @rogeriog & @gbrunin, thanks !