Incorporating Alfvén wave model

[jwreep]

Currently the main copy of HYDRAD does not include the Alfvén wave module. It's a work in progress to update with the latest version of HYDRAD.

It's located on this branch of my fork: https://github.com/jwreep/HYDRAD/tree/Alfven_waves

To incorporate with pydrad, there's a few requirements:

• Add the prepocessor directive ALFVEN_WAVE_HEATING to templates (/Heating_Model/source/config.h primarily)
• Add the template for the wave configuration
• Ensure it works with other preprocessor directives. It doesn't currently depend on others, but the magnetic field needs to be properly incorporated, and this would require USE_POLY_FIT_TO_MAGNETIC_FIELD to be defined simultaneously.