Re-org and add functionality for exporting to Pele and Converge

[d-montgomery]

This is a big PR that includes some breaking changes, new functionality, new tutorials, additional documentation, and renaming/reorganization of files.

Breaking changes:

• GroupContributionMethod.py was renamed FuelLib.py. This was motivated by the name of the repository and the fact that this script contains much more than GCM tools. All imports of GroupContributionMethod must changed as follows:

  # Old import
  import GroupContributionMethod as gcm
  # New import
  import FuelLib as fl
  

• While not entirely necessary, we recommend importing FuelLib as fl instead of gcm. This is consistent with the repo name and will help avoid confusion in the future. This will require searching and replacing all gcm. with fl..
• Mixture functions are now functions of the mass fraction, not mass. This is consistent with the Pele codes and provides the most general approach for predicting mixture properties. All calls to mixture functions will need to have mass replaced with a mass fractions. For example:

  # Old mixture function call for vapor pressure
  mixture_psat = fuel.mixture_vapor_pressure(mass_i, T)
  
  # New mixture function call
  Y_i = mass_i / np.sum(mass_i)
  mixture_psat = fuel.mixture_vapor_pressure(Y_i, T)
  

New functionality:
There are two new scripts in the testing phase for exporting GCM-based predictions to CFD solvers:

• Export4Pele.py: Exports the fundamental GCM predictions for each component for use in the Spray module of PelePhysics.
• Export4Converge: Exports mixture-level predictions over a range of temperatures for use in VOF simulations in Converge.

Reorganization:
The examples have been moved to a directory called tutorials. This coincides with a new tutorials section in the documentation and should provide users a better introduction to FuelLib.

Updated Baseline for Testing:
Minor diffs from converting the mixture property functions from mass-based to mass-fraction-based introduced minor diffs in the baseline tests. The baseline has been reset for future testing based on these changes.