add aggregation function

[ChristopherMancuso]

Add a function so a user can aggregate results across different models

• Does it make sense to do across different gene sets?
• How to handle going across different networks?
• Allow user to supply list of models and autorun?
• Aggregation function takes list or file with folder names, on the user to know what is in there?
• Methods of aggregation, max, mean, ...?
• output is predictions and evaluation?
• Need to save CV fold results and also if gene in test set?