Improved plotting tools

Usage:
    python scatter.py "On-disk f=1, VR f=1, VR f=2"
    data/LOCAL/1000messages_10window_falsevr_1f_1v.csv
    data/LOCAL/1000messages_10window_truevr_1f_1v.csv
    data/LOCAL/1000messages_10window_truevr_2f_1v.csv