Fix get_scoring method

[kxk302]

Currently, get_scoring() in galaxy_ml/utils.py assumes 'secondary_scoring' is a comma separated string. It seems galaxy now provides a list instead. Must revise get_scoring() so it can handle a list and a string (for backward compatibility). Right now, the fix (list to comma separated string conversion) happens in galaxytools. After get_scoring is revised (goeckslab/Galaxy-ML#59), the fix in galaxytools should be removed.