Generalize aggregation per algorithm to support empty pathways with multiple parameter combinations

[ntalluri]

There is now an error with aggregate per algorithm for the ml step. It only runs when for algorithms with multiple parameter combinations chosen; however, some of those parameter combinations can lead to outputs that are all empty, which can lead to the bug error from #117

One solution is using the summary.py file to determine if there are > 1 nonempty files and check that the outputs are all nonempty.