Add OpenMC tutorial

I added the PyMCSim OpenMC tutorial. Note that I made the tutorial use fewer histories and batches for the sake of time and demonstration, but I included the results comparison at the bottom that uses more histories and batches. The full simulation takes a very long time to run (~40 min at least), vs a few minutes for the demonstration set up (this is also important for CI*). I also removed the OpenMC python from sample 0 altogether.

*CI is not setup to run the tutorial test, do you want me to add it to the list?

NOTE: MR 176 should be merged first! I use the changes from that branch in this tutorial. If you want to review this MR separately from those changes before it is merged, the only relevant files are the changes in the tutorial/ folder and test/test_pyarc_run_tutorial.py.