Plot roc and precision recall curves #43

[apoman38]

What this PR does:
3 new functions were added in the train.py file.

1. rep_roc_pr_curves(). Prepare data for plotting roc and precision-recall curves. Specifically, in the function, folders are created where the plots will be stored, and one hot encoding is performed on the labeled data.
2. plot_roc_curve(). Plot roc curves.
3. plot_pre_rec_curve(). Plot precision-recall curves.

How to QA:
Run the train.py file (python3 train.py -v dataset/Aerial dataset/Tilt SVM) and make sure that created two new folders where the plots are saved.