Resolve "Upgrade MC tutorial"

This merge request handles most parts of #243 (closed), but the canonical ensemble is not included (I'd be happy to hand this task to @angqvist who has more experience with it), nor are observers since they seem non-functional at the moment (see #318 (closed))

Description

• The file 5_run_monte_carlo.py has been replaced with two files, 5a_run_monte_carlo_sgc.py and 5b_run_monte_carlo_vcsgc.py. They now run two temperatures (300 and 900 K) instead of three as they did before. They take about 5 minutes each to run.
• The data containers are written to a separate folder (monte_carlo_data) to keep the tutorial folder clean. That folder is included in the repo with the aid of a .gitignore file.
• The analysis has been split in two files.
  • The first (6_collect_monte_carlo_data.py) collects the data in a Pandas dataframe and writes it to a csv file. This might be a bit overkill in this case, but I found this workflow very handy for the AgPd production runs, for which it took a lot of time to just load the data.
  • The second analysis file (7_plot_monte_carlo_data.py) handles plotting. Free energy derivative is plotted for both SGC and VCSGC, mixing energy and acceptance ratio for SGC only.

Comments

The free energy derivative figure is a simplified version of the one in the paper. It looks a bit fishy due to poor sampling, but I suppose short run time of the tutorial scripts trumps the looks of that figure in this case.

A previous comment in the tutorial on discrepancy in critical temperature has been removed because what was said can no longer be read from the graphs.