update to python3

[kkiesling]

VisIt is officially moved over to Python 3. This repo can be updated to make sure it works with VisIt version 3.2+ and python 3.

[kkiesling]

I tried to play around with this this weekend by installing the newest VisIt w/ Python3 and it absolutely still did not work.

I don't have time to work through this, but it might be worthwhile, if this tool is useful to others, to convert it to using Paraview instead of Visit. I did look through the documentation and all the same capabilities seem to be there.