don't hardcode hyper-parameters

[zenalapp]

• For RF: look at Pat's script (lines 46-52): https://github.com/SchlossLab/Sze_SCFACRC_mBio_2019/blob/master/code/rf_classification.R
• LR: hyper-parameters can be passed as argument to function for if we can't figure out a way to automate it
• XGBoost: hyper-parameters can be passed as argument to function for if we can't figure out a way to automate it