[FIX] Rand Forest Class: Min sample replaces max leaf nodes

[BlazZupan]

Random forest for classification had a parameter that in the GUI said "Do not split subsets smaller than", but was actually setting another parameter, max_leaf_nodes. To keep it faithful to the GUI description, the max_leaf_nodes was replaced with min_samples_split, so that now the GUI description matches what the learner actually does.

Minimum to another pruning parameter, max_depth, was changed to 1 (scikit-learn counts this as root plus one more level).

Some minor cleaning of code was also done to line length to 80 and thus get rid of PyCharm warnings.

[codecov-io]

Current coverage is 87.64%

Merging #1403 into master will not change coverage

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