Add pnorm threshold for voting

[davidfee5]

This PR adds an optional network voting probability threshold to reduce low confidence classifications. Only applied to the network vote classifications at this point.

[darren-tpk]

Changes to toolbox.py look good to me.

PNORM_THRESH argument wasn't fed into check_timeline in timeline_checker.py. So I made some changes in the example script. I also note that the example script currently doesn't follow PEP8 recommendations, I'll table that for a separate commit. For now PNORM_THRESH is changed to pnorm_thresh to match the other input args. Will overhaul for PEP8 style later